Patent Grant
7624967
The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Telescoping assemblies such as disclosed in U.S. Pat. No. 5,465,854 are known. Generally, the telescoping tube assembly disclosed in this patent includes a first longitudinal tube section attached to a mounting platform and a second longitudinal section that telescopes relative to the first longitudinal tube section. Additional tube sections can be disposed within each other and within the second longitudinal tube section. Each longitudinal tube section includes a rigid support plate with a U-shaped housing having two spaced-apart longitudinal edges, which attach to the corresponding rigid support plate. Between each longitudinal section are linear bearings or wheels, which allow for the telescopic movement.
In one embodiment, the telescoping tube assembly operates vertically in that the longitudinal tube sections extend and retract downwardly from the first longitudinal tube section. The telescoping action is produced by a drum having a drive cable wrapped therearound and attached to the inner tube section. If the mast has more than one movable tube section, reeving cables or belts can be provided to control movement of each tube section. However, a disadvantage of the above-described assembly is that the use of drive cables limits operation to vertical deployment since the cables can not operate in compression, but only in tension.
In many applications, such as lifting or milling operations, it is necessary that the telescoping tube assembly be able to operate in the presence of compression and tension forces. Drive assemblies have been advanced for telescoping tubes or cranes that used elongated hydraulic cylinder units to extend and retract individual sections. However, as the telescopic assembly increases in size and weight and in the number of moveable sections, the size, weight, number and complexity of hydraulic cylinders increases accordingly. Similarly, other telescopic drive assemblies have used ball-screw assemblies to extend and retract each of the sections, but the size, weight, number and complexity of ball-screw assemblies also increases with the number of moveable sections.
There is thus an ongoing need to provide improved means to operate telescoping assemblies.
This Summary and the Abstract herein are provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary and the Abstract are not intended to identify key features or essential features of the claimed subject matter, nor are they intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.
An opposed-rope driven telescoping mast assembly includes a stationary support and a longitudinal mast comprising a longitudinal section joined to move relative to the stationary support. A drive assembly drives the longitudinal mast and includes a frame and a rotatable drum assembly mounted to the frame. A first rope is joined to the drum assembly and to the longitudinal mast to pull the longitudinal section in a first direction, while a second rope is joined to the drum assembly and to the longitudinal mast to pull the longitudinal section in a second direction. A sensor is operably coupled to the drive assembly to sense overload tension in the first rope or the second rope.
An embodiment of a telescoping mast assembly 10 is schematically illustrated in
A drive assembly 50 extends and retracts the sections 12, 14 relative to each other and the support 20. The sections 12 and 14 are extended and retracted in equal increments thereby exposing substantially the same length of each section during deployment. In other words, if section 12 is extended one foot relative to section 14, then section 14 is also extended one foot relative to support 20. In this manner, overall rigidity of the telescoping assembly 10 is maintained at maximum capability for any position of extension.
To accomplish equal, incremental extension and retraction of the sections, the drive assembly 50 includes a rope and pulley system, which ties the sections 12, 14 together so that moving one section causes proportional movement in the other. Herein “rope” is intended to describe any elongated element that operates or is used in tension. Another form of such an element could be a chain.
In the embodiment illustrated, the wire rope and pulley assembly includes a drum assembly 52 capable of extending and retracting two wire ropes. For example, the drum assembly 52 includes grooved drums 56A, 58A that are joined together so that they turn together. Each drum 56A, 58A controls a wire rope. In particular, the wire ropes comprise a retracting rope 56 and an extending rope 58. The wire ropes 56, 58 are wound in opposite directions on their corresponding drums 56A, 58A. The retracting rope 56 is attached to the bottom of the section 12 and pulls up as the telescoping mast retracts. The retracting rope 56 is guided onto the drum assembly 52 via a pulley 60 provided on the support 20. The retracting rope 56 provides a force for retracting the sections 12, 14.
The extending rope 58 is attached to the top of the section 14 and pulls down on the section 14 as the telescoping mast extends, thereby allowing the mast to apply a downforce to the sections 12, 14 if needed. (A pulley (not shown) but located adjacent to pulley 60 can be used to guide rope 58 to the top of section 14.) Since the section 12 travels twice the distance of the section 14, the drum 56A that drives/controls the section 12 is twice the diameter of the drum 58A that drives/controls the section 14.
A timing rope 80 is attached to the upper end of section 12 and the support 20, but wraps around a pulley 82 provided on the lower end of section 14. The timing rope 80 ensures equal proportional movement of the sections 12, 14 even though section 12 travels twice as fast as section 14 relative to support 20.
As another aspect, the arrangement of the ropes 56, 58 and timing rope 80 is also helpful in that in operation the ropes are in tension; thus, preloading the sections 12 and 14 relative to each other to bring them together. This preload reduces, if not substantially eliminates any meaningful backlash such that the movement of the mast 10 is predictable and accurate.
The drum assemblies and drive motor (not shown in
Mounting components of the drive assembly 50 on the pivoting frame 70 is advantageous. In particular, if the tension in one of the ropes 56, 58 increases due to the telescoping mast encountering an obstruction or an end of travel stop, this causes the drive assembly 50 to move (herein by example, pivot) and trip a suitable switch 72 that can be used to initiate stopping motion of the telescoping mast. Since the ropes 56, 58 pull in opposite directions, this form of overload protection works for both up and down motions of the telescoping mast. In other words, the winding of the ropes 56, 58 in opposite directions causes movement of the drive assembly 50 in one direction only, if an obstruction or end of travel stop is encountered.
In the embodiment illustrated, the extension and retraction overload set points are a function of the distance between the radial distance of the ropes 46, 48 reeling on or off their respective drum and a pivot point 71 of the frame 70. Therefore, in the embodiment illustrated, the overload set points are different. Thus, depending on the configuration of the drums relative to the pivot point 71, the set points can be adjusted individually. Other factors that can be used to adjust the overload set points include the location of the pivot point 71, the weight on frame 70, the length of the frame 70 from the pivot point 71. If desired, additional springs 97 and/or actuator devices 98 (electric, pneumatic, hydraulic) joined to the drive assembly 50 (and to the support 20 schematically) can be used to adjust the overload set points. For instance, the actuator device(s) 98 can be actively controlled by a controller (not shown) such that for extension of the mast 10, the actuator device(s) 98 have a first operating point so as to provide a first overload set point, while for retraction of the mast 10 the actuator device(s) 98 have a second operating point so as to provide a second overload set point. If actuator devices(s) 98 are present movement of components of the actuator devices(s) 98 or other operating parameters such as pressure or electrical voltage and/or current applied can be monitored to sense overload conditions.
Although illustrated with an overload trip switch, other forms of sensing devices, such as but not limited to mechanical, electrical, and/or optical sensing devices, can be used to detect movement of the frame 70, drive assembly 50 or portions thereof. For instance, an angle sensor can be used to measure the angular position of the frame 70 relative to the support 20. In another embodiment, a load cell can be used as an overload switch. One location is as illustrated with load cell 102; however other suitable can be configurations can be used. For instance, a load cell 103 can be used to join the drums 56A, 58A to frame 70, which is represented by load cell 103. In addition, load cells can also be configured in other positions to measure tension in ropes 56, 56 as is known in the art.
Movement of the drive assembly 50, or components thereof also causes both ropes 56, 58 and a timing rope 80 to reach a state of equilibrium when hung vertically. Although the tension in the ropes is not equal, the relationships between the tension in each rope generally remains constant.
In the embodiment illustrated, at least one linear bearing is operatively disposed between sections 12 and 14 and functions as a guiding assembly. Specifically, first linear bearing elements 92A are mounted to an inner surface of housing 14A, while second linear bearing elements 92B that cooperate with the first linear bearing elements 92A are mounted to the housing 12A. Similarly, at least one guiding assembly can be used between section 14 and support 20. In
Furthermore, the telescoping mast assembly 10 can have any number of sections where suitable wire ropes and timing ropes are provided as needed. In addition, the mast assembly 10 need not be telescoping tubes, but rather, the telescoping sections can take any number of forms. For instance, the telescoping sections can be of similar shaped cross-sections of different size, or not be similar such as where one or more sections are tubular and one or more are not tubular. The telescoping sections can be planar, for example, plate members, but again this is but one other embodiment and should not be considered limiting.
Aspects described above can also be applied to a single moving section mast, which is illustrated in
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not limited to the specific features or acts described above as has been held by the courts. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/793,131, filed Apr. 19, 2006, which is hereby incorporated by reference in its entirety.
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