Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
1999-09-27
2001-10-02
Worrell, Danny (Department: 3765)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C051S295000, C051S295000
Reexamination Certificate
active
06295799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to elevator systems, and more particularly to tension members for such elevator systems.
2. Prior Art
A conventional traction elevator system includes a car, a counterweight, two or more ropes interconnecting the car and counterweight, a traction sheave to move the ropes, and a machine to rotate the traction sheave. The ropes are formed from laid or twisted steel wire and the sheave is formed from cast iron. The machine may be either a geared or gearless machine. A geared machine permits the use of higher speed motor, which is more compact and less costly, but requires additional maintenance and space.
Although conventional round steel ropes and cast iron sheaves have proven very reliable and cost effective, there are limitations on their use. One such limitation is the traction forces between the ropes and the sheave. These traction forces may be enhanced by increasing the wrap angle of the ropes or by undercutting the grooves in the sheave. Both techniques reduce the durability of the ropes, however, as a result of the increased wear (wrap angle) or the increased rope pressure (undercutting). Another method to increase the traction forces is to use liners formed from a synthetic material in the grooves of the sheave. The liners increase the coefficient of friction between the ropes and sheave while at the same time minimizing the wear of the ropes and sheave.
Another limitation on the use of round steel ropes is the flexibility and fatigue characteristics of round steel wire ropes. Elevator safety codes today require that each steel rope have a minimum diameter d (d
min
=8 mm for CEN; d
min
=9.5 mm (⅜″) for ANSI) and that the D/d ratio for traction elevators be greater than or equal to forty (D/d≧40), where D is the diameter of the sheave. This results in the diameter D for the sheave being at least 320 mm (380 mm for ANSI). The larger the sheave diameter D, the greater torque required from the machine to drive the elevator system.
Another drawback of conventional round ropes is that the higher the rope pressure, the shorter the life of the rope. Rope pressure (P
rope
) is generated as the rope travels over the sheave and is directly proportional to the tension (F) in the rope and inversely proportional to the sheave diameter D and the rope diameter d (P
rope
≈F/(Dd). In addition, the shape of the sheave grooves, including such traction enhancing techniques as undercutting the sheave grooves, further increases the maximum rope pressure to which the rope is subjected.
The above art notwithstanding, scientists and engineers under the direction of Applicants' Assignee are working to develop more efficient and durable methods and apparatus to drive elevator systems.
SUMMARY OF THE INVENTION
According to the present invention, a preferred tension member for an elevator has an aspect ratio of greater than one, where aspect ratio is defined as the ratio of tension member width w to thickness t (Aspect Ratio=w/t). In another aspect of the invention ropes other than flat ropes (such as round ropes) are benefited by one of the configurations of the invention.
A feature of one embodiment of the present invention is the flatness of the tension member. The increase in aspect ratio results in a tension member that has an engagement surface, defined by the width dimension, that is optimized to distribute the rope pressure. Therefore, the maximum pressure is minimized within the tension member. In addition, by increasing the aspect ratio relative to a round rope, which has an aspect ratio equal to one, the thickness of the tension member may be reduced while maintaining a constant cross-sectional area of the tension member.
According further to the present invention, the tension member includes a plurality of individual load carrying cords encased within a common layer of coating. The coating layer separates the individual cords and defines an engagement surface for engaging a traction sheave.
Due to the configuration of the tension member, the rope pressure may be distributed more uniformly throughout the tension member. As a result, the maximum rope pressure is significantly reduced as compared to a conventionally roped elevator having a similar load carrying capacity. Furthermore, the effective rope diameter ‘d’ (measured in the bending direction) is reduced for the equivalent load bearing capacity. Therefore, smaller values for the sheave diameter ‘D’ may be attained without a reduction in the D/d ratio. In addition, minimizing the diameter D of the sheave permits the use of less costly, more compact, high speed motors as the drive machine without the need for a gearbox.
In a particular embodiment of the present invention, the individual cords are formed from strands of metallic material, organic fiber material or a combination of both. By incorporating cords having the weight, strength, durability and, in particular, the flexibility characteristics of appropriately sized and constructed materials into the tension member of the present invention, the acceptable traction sheave diameter may be further reduced while maintaining the maximum rope pressure within acceptable limits. As stated previously, smaller sheave diameters reduce the required torque of the machine driving the sheave and increase the rotational speed. Therefore, smaller and less costly machines may be used to drive the elevator system.
In order to further enhance tension member service life, the individual cords employed in the invention are treated to avoid fretting. This treatment occurs at two levels. First, the outer strands use wires that are more narrow than the central strand. Because of this difference, a gap is formed between the outer strands. The rope jacket when being formed around the desired number of cords therefore penetrates into the gap between the outer strands to a sufficient degree to prevent strand-to-strand contact and avoid fretting. This is effective and provides for a long flexible tension member service life. It is also a teaching of the invention however, to provide an even longer life or higher weight rated tension member. To this end, the invention teaches to provide a polymer jacket around the central strand in each cord before the outer strands are wound around the central strand. By so doing, contact between the outer strands and the center strand in each cord is diminished and fretting therebetween does not occur. This allows either for a higher weight carrying capacity for the tension member employing this technology or for a longer service life of such tension member. In either case, the industry is substantially benefited. Coating an inner strand in accordance with the invention is applicable to all tension members including but not limited to flat tension members and round tension members. Since flat tension members may be preferred for other reasons the invention is discussed with respect to these. Those of skill in the art will be enabled herefrom to practice the invention on flat or round tension members (or other shape).
Although described herein as primarily a traction device for use in an elevator application having a traction sheave, the tension member may be useful and have benefits in elevator applications that do not use a traction sheave to drive the tension member, such as indirectly roped elevator systems, linear motor driven elevator systems, or self-propelled elevators having a counterweight. In these applications, the reduced size of the sheave may be useful in order to reduce space requirements for the elevator system. The foregoing and other objects, features and advantages of the present invention become more apparent in light of the following detailed description of the exemplary embodiments thereof, as illustrated in the accompanying drawings.
REFERENCES:
patent: 975790 (1910-11-01), Pearson
patent: 1011423 (1911-12-01), Gale, Sr.
patent: 1035230 (1912-08-01), Pearson
patent: 1164115 (1915-12-01), Pearson
patent: 3885380 (1975-05-01), Hacke
Otis Elevator Company
Worrell Danny
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