Elevator – industrial lift truck – or stationary lift for vehicle – Having specific force transmitting connection for... – Equalizes tension in – or length of – plural linking cables
Reexamination Certificate
1999-06-17
2001-05-01
Lillis, Eileen D. (Department: 3652)
Elevator, industrial lift truck, or stationary lift for vehicle
Having specific force transmitting connection for...
Equalizes tension in, or length of, plural linking cables
Reexamination Certificate
active
06223862
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to devices and methods for tensioning cables in an elevator hoist system.
BACKGROUND
Elevator cars, which are roped or cabled in a 2:1 configuration, are supported by wire cables which terminate at each end in thimble rods which are attached to supporting hitch plates located at the top of the elevator hoist way and supported by the building structure. With reference to
FIG. 1
, a typical roping for an elevator car is shown. As shown and described hereinafter, from the supporting hitch plate located above the elevator car, the cables pass under a sheave attached to the elevator car, over a traction drive and guide sheave, under a sheave attached to a counterweight and then back to a second hitch plate located above the counterweight.
As is known, the cables and drive sheaves wear and the cables stretch through normal use. The stretching lengthens the cables which means that certain cables must slip around the sheaves and pulleys to keep up with other cables which may stretch at a different rate. This wears on the traction surfaces of the traction drive sheaves and other sheaves in the system.
If the cable tension is not occasionally adjusted, and the wear and stretching become severe, the entire cable system including the sheaves must be “re-roped.” This requires that the elevator car be taken out of service for a period of time inconveniencing the buildings customers. Further the labor and equipment costs involved in “re-roping” an elevator system are high. Hence it is known to provide periodic service to monitor and adjust the tension of the cables in the elevator system.
One technique to measure the tension of an elevator cable involves a device that hooks onto the cable and by bending the cable measures the cables tension. To adjust the tension of the cables to be substantially equal, the serviceman would measure the tension and adjust each cable at the hitch plate by adjusting the position of the thimble rods relative thereto until each cable tension is substantially the same, i.e. the load carried by each cable is substantially equal. Once the cable tension is adjusted, the car is cycled up and down and the tension checked again to make sure that the tension for the cables is substantially equal. As can be appreciated, this procedure is time consuming and is not entirely accurate.
Another technique is to “pluck” the cables and measure the wave oscillations of the cable which are related to the cables tension. By adjusting the cables in the manner described above and checking the tension, the tension for all cables in the system can be equalized. Again this is time consuming and not highly accurate. Further, whichever technique is used, usually the elevator car must be cycled up and down after each adjustment and the cable tension tested again to confirm that the tensions are substantially equal.
To attempt to resolve the drawbacks noted above, it has been known to install permanent cable tension equalizing mechanisms at the coupling of the thimble rods to the hitch plates. One such example is described in Beatty, U.S. Pat. No. 2,385,488 which uses a hydraulic cylinder in the hitch assembly to connect the elevator cables to the building support structure. Beatty requires that the hydraulic cylinder remain in service and become a permanent part of the hitching assembly which increases the cost of the elevator cable systems. Furthermore, for those systems which were not installed with hydraulic tension equalizers, retrofitting can be expensive, time consuming and may be, depending upon the application, inappropriate.
Other similar approaches to addressing the problem of elevator cable tension by a permanent tension equalizing device are described in Wilson, U.S. Pat. No. 2, 001,007, Hawkins, U.S. Pat. No. 1,516,727.
There is a need for a device and method which can be used to easily and quickly to adjust the tension of elevator cables without replacing or requiring elaborate hitching assemblies. More particularly, there is a need for a device and method which is portable and can be used by service personnel on existing and varying hitching assemblies to quickly and easily adjust cable tension.
SUMMARY OF THE INVENTION
There is, therefore, set forth according to the present invention, a cable tensioning device and method which is portable, is adapted to be coupled to a variety of existing cable hitching assembly configurations and which can be used to easily, accurately and quickly adjust cable tension in an elevator cable system.
The device according to the present invention includes a stand having a platform adapted to be disposed and located above the elevator cable hitching assembly and its thimble rods. A plurality of hydraulic cylinders is disposed and supported on the platform, each cylinder coupled to a thimble rod. Means are provided for supplying pressurized hydraulic fluid to the hydraulic cylinders at substantially equal pressure to impose an equal force upon each cable until the load on each cable is transferred from the hitching assembly to the stand and each cable is under substantially the same tension. At this point, an adjustment is made to secure the thimble rods to the hitching plate while the rods are at substantially equal tension. Thereafter, the hydraulic cylinders are depressurized transferring the load back from the stand to the hitching assemblies. At this point, each of the elevator cables is at substantially the same tension.
If desired, the elevator car may be cycled while the load is being carried by the stand to assure that each of the cables is at substantially the same tension.
The method according to the present invention includes attaching to each thimble rod a hydraulic actuator supported by a stand. Hydraulic fluid is supplied to each actuator to impose an equal force upon the cable to transfer the load from the hitch plate to the stand. Thereafter, each cable is adjusted to the hitch plate while the cables are at substantially equal tension and thereafter the hydraulic fluid is vented from the actuators to transfer the cable load back to the hitch plate. The actuators are then disconnected form the rods.
As can be appreciated, the device and method can be embodied as a small, portable unit taken by the serviceman to the elevator room and used to quickly and accurately adjust the tension of cables in an elevator cable system.
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Chin Paul T.
Lillis Eileen D.
Quirk & Tratos
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