Patent Application
20090107776
The present invention relates to elevator systems, and more particularly to tension members for such elevator systems.
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 (dmin=8 mm for CEN, dmin=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 (Prope) 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 (Prope≈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.
According to the present invention, a 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).
A principal feature 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.
As a result of 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. 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 a further particular embodiment of the present invention, a traction drive for an elevator system includes a tension member having an aspect ratio greater than one and a traction sheave having a traction surface configured to receive the tension member. The tension member includes an engagement surface defined by the width dimension of the tension member. The traction surface of the sheave and the engagement surface are complementarily contoured to provide traction and to guide the engagement between the tension member and the sheave. In an alternate configuration, the traction drive includes a plurality of tension members engaged with the sheave and the sheave includes a pair of rims disposed on opposite sides of the sheave and one or more dividers disposed between adjacent tension members. The pair of rims and dividers perform the function of guiding the tension member to prevent gross alignment problems in the event of slack rope conditions, etc.
In a still further embodiment, the traction surface of the sheave is defined by a material that optimizes the traction forces between the sheave and the tension member and minimizes the wear of the tension member. In one configuration, the traction surface is integral to a sheave liner that is disposed on the sheave. In another configuration, the traction surface is defined by a coating layer that is bonded to the traction sheave. In a still further configuration, the traction sheave is formed from the material that defines the traction surface.
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.
Illustrated in
The tension member 22 and sheave 24 are illustrated in more detail in
In a preferred embodiment, referring to
It is important to the success of the invention to employ wire 29 of a very small size. Each wire 29 and 31 are less than 0.25 millimeters in diameter and preferably is in the range of about 0.10 millimeters to 0.20 millimeters in diameter. In a particular embodiment, the wires are of a diameter of 0.175 millimeters in diameter. The small sizes of the wires preferably employed contribute to the benefit of the use of a sheave of smaller diameter. The smaller diameter wire can withstand the bending radius of a smaller diameter sheave (around 100 millimeters in diameter) without placing too much stress on the strands of the flat rope. Because of the incorporation of a plurality of small cords 26, preferably about 1.6 millimeters in total diameter in this particular embodiment of the invention, into the flat rope elastomer, the pressure on each cord is significantly diminished over prior art ropes. Cord pressure is decreased at least as n−1/2 with n being the number of parallel cords in the flat rope, for a given load and wire cross section.
In an alternate embodiment, referring to
In a third embodiment of the invention, referring to
The cords 26 are equal length, are approximately equally spaced widthwise within the coating layer 28 and are arranged linearly along the width dimension. The coating layer 28 is formed from a polyurethane material, preferably a thermoplastic urethane, that is extruded onto and through the plurality of cords 26 in such a manner that each of the individual cords 26 is restrained against longitudinal movement relative to the other cords 26. Transparent material is an alternate embodiment which may be advantageous since it facilitates visual inspection of the flat rope. Structurally, of course, the color is irrelevant. Other materials may also be used for the coating layer 28 if they are sufficient to meet the required functions of the coating layer: traction, wear, transmission of traction loads to the cords 26 and resistance to environmental factors. It should further be understood that if other materials are used which do not meet or exceed the mechanical properties of a thermoplastic urethane, then the additional benefit of the invention of dramatically reducing sheave diameter may not be fully achievable. With the thermoplastic urethane mechanical properties the sheave diameter is reducible to 100 millimeters or less. The coating layer 28 defines an engagement surface 30 that is in contact with a corresponding surface of the traction sheave 24.
As shown more clearly in
The overall dimensions of the tension member 22 results in a cross-section having an aspect ratio of much greater than one, where aspect ratio is defined as the ratio of width w to thickness t1 or (Aspect Ratio=w/t1). An aspect ratio of one corresponds to a circular cross-section, such as that common in conventional round ropes. The higher the aspect ratio, the more flat the tension member 22 is in cross-section. Flattening out the tension member 22 minimizes the thickness t1 and maximizes the width w of the tension member 22 without sacrificing cross-sectional area or load carrying capacity. This configuration results in distributing the rope pressure across the width of the tension member 22 and reduces the maximum rope pressure relative to a round rope of comparable cross-sectional area and load carrying capacity. As shown in
The separation s between adjacent cords 26 is dependant upon the materials and manufacturing processes used in the tension member 22 and the distribution of rope stress across the tension member 22. For weight considerations, it is desirable to minimize the spacing s between adjacent cords 26, thereby reducing the amount of coating material between the cords 26. Taking into account rope stress distribution, however, may limit how close the cords 26 may be to each other in order to avoid excessive stress in the coating layer 28 between adjacent cords 26. Based on these considerations, the spacing may be optimized for the particular load carrying requirements.
The thickness t2 of the coating layer 28 is dependant upon the rope stress distribution and the wear characteristics of the coating layer 28 material. As before, it is desirable to avoid excessive stress in the coating layer 28 while providing sufficient material to maximize the expected life of the tension member 22.
The thickness t3 of the coating layer 28 is dependant upon the use of the tension member 22. As illustrated in
The diameter d of the individual cords 26 and the number of cords 26 is dependent upon the specific application. It is desirable to maintain the thickness d as small as possible, as hereinbefore discussed, in order to maximize the flexibility and minimize the stress in the cords 26.
Referring back to
Although illustrated as having a liner 42, it should be apparent to those skilled in the art that the tension member 22 may be used with a sheave not having a liner 42. As an alternative, the liner 42 may be replaced by coating the sheave with a layer of a selected material, such as polyurethane, or the sheave may be formed or molded from an appropriate synthetic material. These alternatives may prove cost effective if it is determined that, due to the diminished size of the sheave, it may be less expensive to simply replace the entire sheave rather than replacing sheave liners.
The shape of the sheave 24 and liner 42 defines a space 54 into which the tension member 22 is received. The rims 44 and the flanges 52 of the liner 42 provide a boundary on the engagement between the tension member 22 and the sheave 24 and guide the engagement to avoid the tension member 22 becoming disengaged from the sheave 24.
An alternate embodiment of the traction drive 18 is illustrated in
Alternative construction for the traction drive 18 are illustrated in
Use of tension members and traction drives according to the present invention may result in significant reductions in maximum rope pressure, with corresponding reductions in sheave diameter and torque requirements. The reduction in maximum rope pressure results from the cross-sectional area of the tension member having an aspect ratio of greater than one. The calculation for approximate maximum rope pressure (slightly higher due to discreteness of individual cords) is determined as follows:
P
max≡(2F/Dw)
Where F is the maximum tension in the tension member. For a round rope within a round groove, the calculation of maximum rope pressure is determined as follows:
Pmax≡(2F/Dd)(4/π)
The factor of (4/π) results in an increase of at least 27% in maximum rope pressure, assuming that the diameters and tension levels are comparable. More significantly, the width w is much larger than the cord diameter d, which results in greatly reduced maximum rope pressure. If the conventional rope grooves are undercut, the maximum rope pressure is even greater and therefore greater relative reductions in the maximum rope pressure may be achieved using a flat tension member configuration. Another advantage of the tension member according to the present invention is that the thickness t1 of the tension member may be much smaller than the diameter d of equivalent load carrying capacity round ropes. This enhances the flexibility of the tension member as compared to conventional ropes.
Although the invention has been shown and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that various changes, omissions, and additions may be made thereto, without departing from the spirit and scope of the invention.
This is a continuation-in-part of U.S. Ser. No. 09/031,108 filed Feb. 26, 1998, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10839550 | May 2004 | US |
| Child | 11981346 | US | |
| Parent | 09218990 | Dec 1998 | US |
| Child | 10839550 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09031108 | Feb 1998 | US |
| Child | 09218990 | US |
