BACKGROUND OF THE INVENTION
The present invention relates to a cable or rope for use in drive lines of theatrical rigging systems.
SUMMARY OF THE INVENTION
In power assisted counterweight theatrical rigging systems, it is preferable to use loft blocks and head blocks of the same size as in a manual counterweight rigging system. According to one power assisted counterweight rigging system disclosed in pending U.S. patent application Ser. No. 11/532,975, which is assigned to the assignee of this application, the drive line of the system is comprised of a combination of drive chain and rope or cable. In such a system, the drive chain is used to ensure that the rotary motion of the drive motor is efficiently transmitted to the drive line. Operation of the chain drive in such a system can produce extraneous noise, which is undesirable in a theatrical environment. In addition, the chains used in chain drive systems are heavier than rope of a comparable length and the combination of chain and rope drive in the drive line requires rope-to-chain transition connectors.
It is therefore a principal object and advantage of the present invention to provide an efficient drive system for a power assisted counterweight rigging system that does not involve the extraneous noise associated with chain drive mechanisms. It is a further objective of the present invention to provide a drive line that is lighter than a chain-rope combination and has no requirement for rope-to-chain connectors.
In accordance with the foregoing objects and advantages, the present invention provides a flexible drive rope comprising a core of natural fiber, synthetic fiber, or metallic material. The core is surrounded by a layer of flexible material that includes traction features. Also disclosed is a drive pulley that contains traction features that correspond to the traction features of the drive rope. Accordingly, the drive rope and drive pulley co-operate to provide an efficient, but generally quiet drive system that can be connected to a variety of drive motors and used with counterweight rigging systems that have been retrofitted to use a motor.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:
FIG. 1 is a partial sectional view of a drive rope according to an embodiment of the invention;
FIG. 2 is an elevation view of a drive pulley corresponding to the drive rope of FIG. 1;
FIG. 3 is a partial sectional view of a drive rope according to another embodiment of the invention;
FIG. 4 is an elevation view of a drive pulley corresponding to the drive rope of FIG. 3;
FIG. 5 is a partial sectional view of a drive rope according to another embodiment of the invention; and
FIG. 6 is an elevation view of a drive pulley corresponding to the drive rope of FIG. 5.
DETAILED DESCRIPTION
Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in FIG. 1 a drive rope 10. Drive rope 10 has a core 12 of high strength fiber or flexible metal cable. Suitable materials for the core 12 include aramid fiber, steel or other equivalent materials known to those of ordinary skill in the art. Core 12 may comprise multiple braided or twisted elements. Core 12 also may be comprised of plastic or polymer material that has been mixed with non-contiguous linear or fibrous elements to enhance its tensile strength. In the preferred embodiment, core 12 is comprised of ⅜″ steel cable. Core 12 is surrounded by jacket 14. The material of jacket 14 may also occupy interstitial spaces within core 12. Jacket 14 is comprised of flexible material, such as polyurethane or another equivalent plastic. Jacket 14 must be sufficiently flexible and elastic that it can wrap around the pulleys of a counterweight rigging system without cracking. In the preferred embodiment, jacket 14 is comprised of a 3/16″ layer of polyurethane. Drive rope 10 also includes traction elements on its outer surface consisting primarily of features 16 molded into or bonded onto jacket 14. The features 16 preferably are positioned in a consistent cross-woven pattern such that crossing points 18 are consistently and evenly spaced along the length of drive rope 10. The preferred embodiment has a nominal outside diameter of ¾″, which makes it suitable for use with standard headblocks used in counterweight rigging systems. According to one embodiment, features 16 are raised above the surface of jacket 14. Alternatively, features 16 may be depressed below the surface of jacket 14.
There is shown in FIG. 2 a drive pulley 20. Drive pulley 20 is in many respects a conventional pulley that can be operatively connected to a drive motor (not shown) to transmit the drive motor's rotary motion to a drive rope such as the one depicted in FIG. 1. Around its perimeter, pulley 20 includes a U-shaped groove 22. U-shaped groove 22 includes in its surface a plurality of traction grooves 24. Traction grooves 24 are sized and positioned to match the pattern formed by features 16 of drive rope 10. In this way, features 16 engage traction grooves 24 to increase the traction between drive pulley 20 and drive rope 10. In an alternate embodiment, traction grooves 24 can consist of raised features that correspond to features 16 that are depressed into the surface of jacket 14.
There is shown in FIG. 3 another embodiment of the invention, consisting of drive rope 10′ having a core 12′ of high strength synthetic or natural fiber, steel or similar material. Core 12′ is surrounded by jacket 14′. Jacket 14′ is comprised of flexible material, such as polyurethane or another equivalent plastic. Jacket 14′ must be sufficiently flexible and elastic that it can wrap around the pulleys of a counterweight rigging system without cracking. Drive rope 10′ also includes traction elements on its outer surface consisting primarily of a spiral-wrapped feature 16′ molded on or bonded onto jacket 14′. The spiral-wrapped feature 16′ is positioned in a consistent, regular spiral pattern such that each wrap (or thread) 18′ is consistently and evenly spaced along the length of drive rope 10′.
There is shown in FIG. 4 a drive pulley 20′. Drive pulley 20′ is in many respects a conventional pulley that can be operatively connected to a drive motor (not shown) to transmit the drive motor's rotary motion to a drive rope such as the one depicted in FIG. 3. Around its perimeter, pulley 20′ includes a U-shaped groove 22′. U-shaped groove 22′ includes in its surface a plurality of traction grooves 24′. Traction grooves 24′ are sized and positioned to match the pattern formed by spiral-wrapped cord 16′ of drive rope 10′. In this way, spiral-wrapped cord 16′ engages traction grooves 24′ to increase the traction between drive pulley 20′ and drive rope 10′.
There is shown in FIG. 5 another embodiment of the invention, consisting of drive rope 10″ having a core 12″ of high strength s synthetic or natural fiber, steel or similar material. Core 12″ is surrounded by jacket 14″. Jacket 14″ is comprised of flexible material, such as polyurethane or another equivalent plastic. Jacket 14″ must be sufficiently flexible and elastic that it can wrap around the pulleys of a counterweight rigging system without cracking. Drive rope 10″ also includes traction elements on its outer surface consisting primarily of ridges 16″ formed in the surface of jacket 14″. Ridges 16″ can be formed by adding material to jacket 14″ to form each ridge 16″, or by molding depressions into the surface of jacket 14″ such that a ridge 16″ is formed on either side of the depressions. Ridges 16″ are positioned in a consistent, regular pattern such that each ridge 16″ is consistently and evenly spaced along the length of drive rope 10″. According to this embodiment, the outer diameter of ridges 16″ is approximately ¾″ in diameter to match the size of the drive rope conventionally used in a counterweight rigging system. If a particular counterweight rigging system is designed to operate with rope of a different size, it is readily recognized that drive rope 10″ can be fashioned in a variety of sizes.
There is shown in FIG. 6 a drive pulley 20″. Drive pulley 20″ is in many respects a conventional pulley that can be operatively connected to a drive motor (not shown) to transmit the drive motor's rotary motion to a drive rope such as the one depicted in FIG. 5. Around its perimeter, pulley 20″ includes a U-shaped groove 22″. U-shaped groove 22″ includes in its surface a plurality of traction grooves 24″. U-shaped groove 22″ is sized to accept drive rope 10″. Traction grooves 24″ are sized and positioned to match the pattern formed by ridges 16″ of drive rope 10″. In this way, ridges 16″ engage traction grooves 24″ to provide positive traction between drive pulley 20″ and drive rope 10″.
Traction features 16, 16′ and 16″ can be used to index the drive line position of drive rope 10, 10′, 10″. The positive traction between the drive pulleys and drive ropes of the present invention eliminates slippage between drive rope and drive pulley; each turn of a drive pulley results in linear movement of the drive rope for a distance of πD (where D is the pitch diameter of the drive pulley). Because of the positive traction, systems used to control the position of a load suspended from the rigging system can be calibrated to calculate the vertical position of the load based on rotation of the drive pulley.
Patent Grant
7971856
