Patent Application
20100037436
An elevator is a hoisting and lowering mechanism equipped with a car or platform which moves in guides in a vertical direction. Traction elevator systems typically include a cab, a counterweight, one or more ropes interconnecting the cab and counterweight, a traction sheave to move the rope(s), and a motor to rotate the traction sheave. Elevator ropes conventionally comprise laid or twisted steel wire and the sheave is formed of cast iron.
Electric elevators are suspended and moved by a series of pulleys (sheaves) and cables (ropes). In a typical arrangement, a wire rope is reeved over a number of sheaves, terminating in a hitch on the top and bottom of the car. Care is typically taken during the installation to mount the various sheaves in the machine room or on the car in such a manner as to ensure only vertical strain is applied to the wire ropes terminating in hitches. This reduces metal fatigue on the wire rope that would occur if subjected to horizontal bending forces.
Tensile strength measures the stress required to pull something such as rope, wire, or a structural beam to the point where it breaks. It is an intensive property of the material. The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before failure. There are three typical definitions of tensile strength: (1) yield strength, which is the stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently; (2) ultimate strength, which is the maximum stress a material can withstand; and (3) breaking strength, which is the stress coordinate on the stress-strain curve at the point of rupture. The tensile strength of an elevator rope system is often at its weakest point at the termination of the elevator rope. The uniform forces on the rope along the wedge effectively lock the rope in the termination. As the rope tension increases, the differential compressive forces at the nose of the termination will also increase accordingly.
For example, a rope having a rated breaking strength of 25,000 lbs may be limited by the termination device, which may reduce the overall breaking strength of the system to a fraction of the percentage, such as 65% of the rope itself. According to the European code (EN81), the minimum required breaking strength of the termination is 85% of the full breaking strength of the rope. If the rope termination is only 65% of the breaking strength of the rope, the rope will have to be rated at a lower number to meet this requirement.
Coated steel belts (CSB's) have been developed which are strong enough to replace the traditional wire cables used with elevators. These CSB's permit sheave and hitch arrangements that were not practical when using wire ropes. In an arrangement where the CSB hitch or termination is subjected to horizontal forces as well as vertical forces, metal fatigue is a concern. Conventional steel ropes and the cast iron sheaves that move them have certain limitations in their use. One such limitation is the traction forces between the ropes and the sheave. Drive sheaves with large diameters are often needed to obtain the required traction to move the components in the system without the rope slipping over the sheave. Another limitation on the use of steel ropes is the flexibility and fatigue characteristics of steel wire ropes. Aramid-based ropes are being developed to overcome the problems associated with steel cables. Conventional termination devices, however, do not readily lend themselves to use with aramid-based ropes, where aramid-based ropes tend to slip out of such devices and, consequently, a dangerous condition may result. Furthermore, termination devices may reduce the overall breaking strength of the elevator rope system such that more rope will be needed to meet the minimum safety factor.
Accordingly, there is a need for a termination device that can accommodate aramid-based elevator ropes. It would be further advantageous to provide a termination device to accommodate aramid-based elevator ropes that minimally reduces the breaking strength of the overall system. It would be further advantageous to provide a termination device that reduces the breaking strength of a rope by 85% or less to avoid such that the rope will no longer need to be rated at a lower breaking strength and less rope can be used for a specific application.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown. In the drawings, like reference numerals refer to like elements in the several views. In the drawings:
Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.
Disclosed is a termination device for an aramid-based elevator rope having a high breaking strength. In one version, the termination device comprises a socket having a cylindrical, tapered internal passageway adapted to receive a corresponding wedge. The wedge includes a semi-cylindrical passageway in a substantially helical configuration to increase the surface area between the associated rope and the wedge. The termination device clamps the length of rope between tapered portions of the socket and the semi-cylindrical passageway of the wedge with a substantially uniform application of force on the cross-section of the rope. The termination uniformly distributes the compression force along the entire length of the termination. This uniform compression force is set such that it will neither crush the rope nor allow the rope will slip out of the termination.
Referring now to the drawings in detail, wherein like numerals indicate the same elements throughout the views,
The tension member or rope 60 shown in
Referring to
Still referring to
Referring to
As illustrated in
The peripheral groove 103 is divided into an upper portion 110 and a lower portion 105 having a substantially helical shape. The helical configuration is described by way of example only, where any suitable configuration that extends the contact surface area between the rope and termination is contemplated.
The upper portion 110 is configured to accept the rope 60 as it passes from the central bore. After exiting the bore 115 the rope 60 is wound around both the upper portion 110 and lower portion 105 of the wedge 100. The large radius of the top portion is to allow the rope to wrap around wedge without carrying majority of the load.
After the rope 60 has been fitted into the peripheral groove 103 the wedge 100 is urged into the socket 90 such that the wedge 100 and socket engage in a luer slip relationship. In one version, the rope is fully wrapped around the wedge prior to the assembly.
In the assembled configuration, the rope 60 passes through the front opening 93 of the socket, through the bore 115 of the wedge, and around the peripheral groove 103 of the wedge 100. The live end of the rope, which passes through the bore 115, is connected to another component in the elevator system, such as a sheave, whereas the dead end of the rope 143 does not bear a load. The wedge 100 may be formed from any material which will retain its structural integrity and can keep the rope 60 secured in the termination device 80 without slippage. In one version the wedge 100 is constructed of polished steel. It will be appreciated that any suitable material, such as cast iron, may be used.
In summary, numerous benefits have been described which result from employing the concepts of the invention. The foregoing description of one or more embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The one or more embodiments were chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
