A crane comprising a boom formed as an elongate tubular structure and a line assembly to extend a line from a least one end of the boom. The line assembly may include a first bank of sheaves, a second bank of sheaves, a line reeved around the first and second banks of sheaves, and an extension mechanism controlling the distance between the first and second banks of sheaves. The second bank of sheaves and at least a portion of the extension mechanism being enclosed within boom.

BACKGROUND

1. The Field of the Invention

This invention relates to lifting devices and, more particularly, to novel systems and methods related to live-line cranes.

2. The Background Art

Live-line lifting devices are machines capable of dispensing and retracting a length of line. Such devices are typically used to manipulate objects too massive to safely manipulate manually. Many current live-line lifting devices employ a winch that winds and unwinds a cable. These winches are typically driven by electric or hydraulic motors. Accordingly, they have certain disadvantages.

For example, spooling winches are typically expensive. They occupy a significant amount of space. They require stops to prevent the cable from being wrapped all the way on or off the spool. Moreover, spooling winches decrease in lifting capacity as the cable is wound onto the spool. That is, the winch produces a constant torque, but the moment arm acting against the winch increases as cable wraps around the spool and increases its diameter. Accordingly, current winch devices may begin lifting a heavy object, but fail or stall once the object has been lifted to a certain point. This increase in diameter also causes an increase in the speed at which cable is retracted, even while the winch operates at a constant rotational velocity

Accordingly, what is need is a live-line lifting device that is compact and inexpensive to manufacture. Additionally, the device should dispense and retract line at a constant rate when desired. Moreover, the device should support the same maximum load at full retraction of the line that it can at full extension of the line.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, in accordance with the invention as embodied and broadly described herein, a method and apparatus are disclosed in one embodiment of the present invention as including a crane comprising a boom, a base, and a line assembly. A boom may be formed as an elongate tubular structure. In certain embodiments, the boom may be extensible and include an extension and a housing. The extension may be shaped and sized to translate within the housing. A lock may be included to selectively fix the extension with respect to the housing to provide a desired overall length for the boom. In such embodiments, both the extension and the housing may be tubular structures closed on all sides or otherwise.

In general, a boom may extend generally horizontally. Accordingly a base may extend generally vertically to support the boom. In selected embodiments, a base may control the attitude of the boom. For example, a base may include a post and an extension mechanism. Both the post and the extension mechanism may pivotably engage the boom. Accordingly, by increasing or decrease the length of the extension mechanism, the angle of the boom with respect to the horizontal may be controlled.

A line assembly in accordance with the present invention may include a first bank of sheaves, a second bank of sheaves, an extension mechanism, and a line of one form or another. In selected embodiments, the first bank of sheaves may comprise a plurality of sheaves, each positioned to rotate about a particular axis. Similarly, the second bank of sheaves may comprise a plurality of sheaves, each positioned to rotate about a different axis. The extension mechanism may be positioned and configured to control the distance between the first and second banks of sheaves.

In selected embodiments, the line of the line assembly may having a first end, an intermediate portion, and a second end. The first end of the line may be connected to the boom. The intermediate portion of the line may be reeved between the first and second banks of sheaves. The second end of the line may be suspended from the boom proximate an end thereof. By controlling the distance between the first and second banks of sheaves (i.e., the elongation caused by the extension member) the length of line suspended from the boom may be controlled. Accordingly, the crane may be used as a live-line lifting device.

In certain embodiments, a boom may house the line assembly. That is, the line assembly may be enclosed within the tubular structure of the boom or one of its sub-components (e.g., the extension). In such embodiments, one of the first and second banks of sheaves may be designated an idling (stationary) bank. The other may be designated a working (moving) bank. The idling bank may be fixed with respect to the boom. The working bank, on the other hand, may be free to travel longitudinally within the boom at the impetus of the extension member of the line assembly.

By housing the line assembly within the boom, the tubular structures of the boom may maintain the proper alignments and connections of the line assembly as it extends and retracts. The boom may increase the safety of the crane by provide a shroud limiting access to the line assembly with its moving parts and pinch points. Additionally, the aesthetics of the crane may be improved by providing a simple and compact profile, decreasing exposure of cables (wire rope) to weather and rust, hiding greasy components, and so forth.

Accordingly, a crane in accordance with the present invention may provide a live-line lifting device where the speed at which line is consumed or dispensed may be directly proportional to the speed at which the extension mechanism of the line assembly changes the distance between the idling and working banks. Thus, if the extension mechanism of the line assembly changes length at a constant rate, the line will be dispensed at a constant rate. Additionally, virtually any load that may be supported by a crane in accordance with the present invention at the full extension of the line may also be supported at full retraction of the line.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Referring toFIG. 1, in describing a crane10in accordance with the present invention, it may be advantageous to first define longitudinal11a, lateral11b, and transverse11cdirections substantially orthogonal to one another. In general, the longitudinal direction11amay be aligned with the longest dimension of the crane10. The lateral direction11bmay extend from side to side. Accordingly, the transverse direction11cmay be aligned vertically.

The various structures on a crane10in accordance with the present invention may be selected and arranged to perform various functions. For example, in typical use, a crane10may raise and lower objects of significant weight (e.g., humanly impossible, unhealthy, or unsafe to lift directly). Accordingly, a crane10may include a boom12supported by a base14. In general, a boom12may extend in the longitudinal direction11a, while the base14extends in the transverse direction11c.

In selected embodiments, a base14may pivotably secure the boom12to control the attitude thereof. For example, in some embodiments, a base14may include a post16and an extension mechanism18(e.g. a hydraulic cylinder18or the like). Both the post16and the extension mechanism18may pivotably engage the boom12. Accordingly, by increasing or decrease the length of the extension mechanism18, the angle of the boom12with respect to the horizontal may be controlled. In some embodiments, a base14may be supported by a foundation fixable with respect to the ground. In certain embodiments, the foundation may comprise a turntable permitting the base to rotate about a substantially vertical axis.

In certain embodiments, a boom10may house a line assembly20. In operation, the line assembly20may extend and retract a line22(e.g., a rope22, wire rope22, a metallic cable22, two of these or the like). For example, when the line22is retracted into the boom10, a hook24may be pulled toward the boom10. Thus, any load connected to the hook24may be lifted. Alternatively, when the line22is dispensed from the boom10, the hook24and any load attached thereto may be lowered away from the boom10.

A boom12in accordance with the present invention may include an interface26facilitating engagement with the base14. In selected embodiments, an interface26may include one or more interface plates28. The plates28may extend to engage the base14.

Referring toFIGS. 1 and 2, in selected embodiments, a boom12may be adjustable in length to control the reach of the boom12. For example, in some embodiments, a boom12may include a housing30and an extension32. The extension32may be shaped and sized to translate within the housing30. Accordingly, an extension32may translated between a fully extending position providing a maximum length for the boom12and a fully retracted position (as illustrated) providing a minimum length for the boom12. In such embodiments, a boom10may include a lock34selectively fixing the position of the extension32with respect to the housing30. An extension32in accordance with the present invention may be mounted in many different configurations to a variety of other mounting and supporting structures.

A housing30in accordance with the present invention may have any suitable configuration. In selected embodiments, a housing30may be tubular and have a rectangular cross-section. An extension32may have a shape corresponding to the shape of the housing30. Accordingly, in embodiments where the housing30is tubular with a rectangular cross-section, the extension32may also be tubular with a rectangular cross-section.

Referring toFIG. 3, a lock34in accordance with the present invention may operate in any suitable manner. For example, in selected embodiments, a lock34may include a shear pin located on the housing30and biased toward engagement with various apertures36located in the extension32. Accordingly, to disengage the lock34, an operator may manually withdraw the shear pin from the aperture36. The operator may then translate the extension within the housing30until the shear pin aligns with a desired aperture36. Accordingly, the shear pin may be manually or automatically inserted through the aligned aperture36and again fix the extension32with respect to the housing30.

In selected embodiments, an extension32may include one or more slide plates38. These slide plates38may be positioned to fill certain gaps between the extension32and the housing30. Accordingly, the slide plates38may control undesirable motion (e.g., rattling or the like) of the extension32by biasing it or capturing it closely within the housing32. Additionally, the slide plates38may be selected and positioned to reduce frictional forces as an extension32is translated within a housing30. In selected embodiments, slide plates38may be formed of a friction reducing material such as brass, high density polyethylene (HDPE), or the like.

In embodiments having an inextensible boom12, that boom may be patterned after the extension32described herein. That is, in selected embodiments, the boom12may have a single tubular body and include interface plates28for engaging the base14.

In certain embodiments, an extension32may house the line assembly20. Accordingly, an extension32may include a line assembly interface40connecting the line assembly20to the rest of the extension32. For example, a line assembly20may include one or more sheaves rotating about one or more rods42,44. A line assembly interface40may include one or more apertures to received such rods42,44. Accordingly, in some embodiments, securing the rods42,44, the line assembly interface40may effectively connect the line assembly20to the extension32. Multiple lines and multiple assemblies20in a boom may permit, for example a motor lift (hoist) to receive both support and electrical power through two separate lines. What is true for a single bank of sheaves may typically be done in multiple banks, typically in parallel.

Additionally, a line assembly interface40may provide a shroud46covering the sheaves. The shroud46may protect the sheaves as well as any object (e.g., hand, finger, or the like) that may otherwise become entangled therewith. A line assembly interface40may also include a handle48. The handle48may facilitate manual translation of the extension32within the housing30. Additionally, the handle48may provide a location where a static lift line may be secured to the boom12.

Referring toFIGS. 4-8, a line assembly20in accordance with the present invention may include a first bank of sheaves50, a second bank of sheaves52, and an extension mechanism54(e.g., a hydraulic cylinder54or the like) controlling the distance between the first and second banks of sheaves52,54. In general, the first bank of sheaves50may be characterized as an idling bank50, as it may be fixed with respect to the boom12. The second bank of sheaves52may be characterized as a working bank52, as it may travel back and forth under the impetus of the extension mechanism54. In selected embodiments, an extension32may be sized and shaped to guide the working bank52as it is manipulated by the extension mechanism54.

In selected embodiments, an extension mechanism54in accordance with the present invention may be embodied as a hydraulic cylinder. In such embodiments, certain hydraulic hoses may be require access to the cylinder. Such hoses may extend to reach the cylinder in any suitable manner, whether internally or externally with respect to the boom12and base14. In selected embodiments, the base14(e.g., post16) may act a repository housing hose (e.g., flexible hose) sufficient to accommodate any travel of the extension32within the housing30.

A line22may include a first end56, an intermediate portion58, and a second end60. The first end56of the line22may be fixed with respect to the boom12. The intermediate portion58of the line22may be reeved between the idling and working banks50,52. The second end60of the line22may be suspended from the boom12.

In selected embodiments, the idling bank50may be secured, maintained in position, and connected to the extension mechanism54by an idling housing62. In some embodiments, the idling housing62may be secured to the extension32by one or more removable fasteners. The idling housing62may include a base plate64, two cheek plates66, and a rod42.

The base plate64may provide the interface between the cheek plates66and the extension mechanism54. Additionally, the base plate64may provide a location for securing the first end56of the line22. The cheek plates66may be positioned adjacent the lateral faces of the idling bank50. The rod42(e.g., a shoulder bolt42or the like) may pass through the cheek plates66to capture the various sheaves68forming the idling bank50. If desired or necessary, the rod42of an idling housing62may also support one or more washers70positioned to appropriately space the various sheaves68. In some embodiments, the sheaves68may include bearings to facilitate rotation about the rod42.

In selected embodiments, the working bank52may be secured together and connected to the extension mechanism54by working housing72. The working housing72may include a base plate74, two cheek plates76, and a rod78. The base plate74may provide the interface between the cheek plates76and the extension mechanism54. Additionally, the base plate74may provide a location for securing the first end56of the line22.

The cheek plates76may be positioned adjacent the lateral faces of the working bank52. The rod78(e.g., a shoulder bolt78or the like) may pass through the cheek plates76to capture the various sheaves68forming the working bank52. If desired or necessary, the rod78of working housing72may also support one or more washers70positioned to appropriately space the various sheaves68. The sheaves68may include bearings facilitating rotation about the rod78.

In certain embodiments, slide pads80may be included as part of the working housing72. The slide pads80may be positioned to contact with the inner walls of the boom12(e.g., extension32). Accordingly, the pads80may provide a bearing surface as the working housing72travels back and forth within the boom12. In selected embodiments, the slide pads80may be selected and positioned to reduce frictional forces. For example, slide pads80may be formed of a friction reducing material such as brass, high density polyethylene (HDPE), or the like.

Additionally, the slide pads80may control undesirable motion of the working housing72within the boom12. For example, the pads80may assist in aligning the working bank72within the boom12and resist rotation of the extension mechanism54.

In operation, as an extension mechanism54increases and decreases the distance between the idling and working banks50,52, the length of line22necessary to pass from one bank50,52around the other52,50and back correspondingly increases or decreases. As a result, the amount of line22remaining that may be suspended from the boom12may be controlled.

The speed at which line22is consumed or dispensed from a line assembly20may be directly proportional to a multiple of the speed at which the extension mechanism54changes the distance between the idling and working banks50,52. The multiple may be selected with load capacity when selecting or designing line size. Additionally, the loads that may be supported by a line assembly20may be constant throughout the entire range of operation. That is, any load that may be supported by a line assembly20at the full extension of the line22may be supported by that line assembly20at full retraction of the line22. Moreover, if the speed of extension or retraction of the extension mechanism54is constant through its range of operation, then the speed of retraction and extension of the line22will be constant through its range of operation.

The number of sheaves68within the idling and working banks50,52may vary from embodiment to embodiment. An increase in the number of sheaves68may produce an increase in the number of times a line22may be wrapped from one bank50,52around the other52,50and back. As a result, in general, the greater the number of sheaves68, the greater the difference in the length82of suspended line22between the fully retracted position84and the fully extended position86.

In certain embodiments, the number of sheaves68contained in the idling and working banks50,52may be constrained by the size of the boom12into which the line assembly20will be installed. In other embodiments, the number of sheaves68contained in the idling and working banks50,52may be constrained by the maximum force that may safely be generated by the extension mechanism54. That is, by reeving a line22about the idling and working banks50,52, the extension mechanism54may be forced to work against a mechanical disadvantage equaling some multiple of the tension within the line22. Accordingly, at some point, additional wraps of the line22may cause an extension mechanism54to be loaded beyond its capacity.

In one embodiment, a line assembly20where the idling and working banks50each include about four to five sheaves68may be included within a boom12of reasonable size. Additionally, a line assembly20where the idling and working banks50each include about four to five sheaves68may provide sufficient change in the length82of line22suspended from a boom12to function adequately (e.g., about twice the stroke per sheave pair). Moreover, a line assembly20where the idling and working banks50each include about four to five sheaves68may not overly disadvantage the extension mechanism54to a point where it cannot lift expected loads.

In selected embodiments, in may be desirable or necessary to limit the ability of the line22to exit certain sheaves68. Accordingly, a crane10in accordance with the present invention may include any mechanism designed to maintain the line22within the grooves of the sheaves68. In certain embodiments, the clearance88between certain sheaves68and the surrounding structures (e.g., the main tube of the extension32, the shroud46, or the like) may be selected to resist exit of the line22. That is, the clearance88may be sufficiently small that the line22cannot pass therethrough and, therefore, must remain in the groove of the sheave68.

Alternatively, one or more additional structures may be included within a crane10to artificially create a small clearance88. For example, in one embodiment, a rod may pass in the lateral direction11bthrough the shroud46, working housing72, or the like at a location selected to maintain the line22within the respective grooves of the sheaves68.

In certain embodiments, a line assembly20in accordance with the present invention may include a lifting sheave68a. In some embodiments, a lifting sheave68amay be positioned proximate a distal end of the boom12to guide the line22in and out of the boom12. In one embodiment, a lifting sheave68amay be positioned below the idling bank50. In such an embodiment, the lifting sheave68amay be mounted on a rod44. A brace90may connect the rod44corresponding to the lifting sheave68ato the rod42corresponding to the idling bank50.

In selected embodiments, a brace90may include upper spacers92, lower spacers94, and a webbing96connecting the upper spacer92on each side with the lower spacer94corresponding to that side. In some embodiments, each upper spacer92may surround the rod42laterally outside of the cheek plates66of the idling housing50. Similarly, each lower spacer94may surround the rod44on each side of the lifting sheave68. Accordingly, the webbing96may extend from the upper spacers92to the lower spacers94.

Referring toFIG. 9, in selected embodiments, a lifting sheave68amay be omitted. In such embodiments, the line22may be suspended directly from a sheave68of the idling bank50. In such embodiments, if desired or necessary, an additional sheave68may be added to the idling bank50to provide the same line retraction and extension capabilities that may be associated with embodiments including a separate lifting sheave68a. Additionally, the configuration of the shroud46may be adjusted to fit the new geometry of the idling bank50.

Referring toFIG. 10, in selected embodiments, a line assembly20in accordance with the present invention may be positioned somewhere other than within the boom12. For example, in selected embodiments, a line assembly20may be positioned within the base14(e.g., a post16). Accordingly, an extension mechanism54may selectively translate the working bank52within the confines of the base14. In such embodiments, a lifting sheave68amay be positioned at the distal end of the boom12to guide the line22into and out of the boom12. In selected embodiments, a crane10having the line assembly20positioned within the base14may still include an extendable boom12through which the line passes for use. Accordingly, a boom12in such embodiments may include a housing30and an extension32.