A tension member termination device optimized for terminating flat tension members having compressible outer coatings, the device including a wedge and a socket each having cooperating surfaces positioned at a predetermined angle for clamping the tension member therebetween. The angle reliably secures the tension member while avoiding deleterious pressure and stress upon the tension member. The invention also provides a safety clamp for optional use with the tension member termination device.
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1. A termination device for a tension member, the tension member having a width w and an elastomer coating that has a maximum compressive stress capability σc, the tension member being subjected to a tensile force t, the termination device comprising:
a socket; and
a wedge that fits within the socket with the tension member wrapped around the wedge, the wedge having a clamping surface that includes a length l and is disposed at an angle ϕ, which is measured from a centerline of the wedge to the clamping surface and which relates to the length l in accordance with the formula defining a minimum of the angle ϕ:
ϕ≥tan−1 ϕ=tan−1(t/(σc*l*w)). 0. 4. A termination device for a tension member, the tension member having a width w and a compressible coating that has a predetermined maximum compressive stress capability σc, the compressible coating being subject to compressive creep, the tension member being subjected to a tensile force t, the termination device comprising:
a socket; and
a wedge that fits within the socket with the tension member wrapped around the wedge, the wedge having a clamping surface that includes a length l and is disposed at an angle ϕ, which is measured from a centerline of the wedge to the clamping surface and which relates to the length l in accordance with the formula defining a minimum of the angle ϕ:
ϕ=tan−1(t/(σc*l*w)). 2. A method for terminating a tension member having a width w and an elastomer coating that has a maximum compressive stress capability σc, comprising:
feeding the tension member into an aperture of a socket;
wrapping the tension member around a wedge having a clamping surface that includes a length l and is disposed at an angle ϕ, which is measured from a centerline of the wedge to the clamping surface;
feeding the tension member back through the aperture; and
applying a tensile force t in the tension member so that the tension member is compressed between the wedge and the socket, wherein the tensile force t is applied in accordance with the formula defining a minimum of the angle ϕ:
ϕ≥tan−1 ϕ=tan−1(t/(σc*l*w)). 0. 5. A method for terminating a tension member having a width w and a compressible coating that has a predetermined maximum compressive stress capability σc, the compressible coating being subject to compressive creep, the method comprising:
feeding the tension member into an aperture of a socket;
wrapping the tension member around a wedge having a clamping surface that includes a length l and is disposed at an angle ϕ, which is measured between a centerline of the wedge and the clamping surface;
feeding the tension member back through the aperture; and
applying a tensile force t in the tension member so that the tension member is compressed between the wedge and the socket, wherein the tensile force t is applied in accordance with the formula defining a minimum of the angle ϕ:
ϕ=tan−1(t/(σc*l*w)). 0. 6. A termination device for a tension member, the tension member having a width w and comprised of a plurality of inner load carrying cords and a compressible coating, wherein the compressible coating defines a traction surface for the tension member and the compressible coating has a predetermined maximum compressive stress capability σc, the compressible coating being subject to compressive creep if the maximum compressive stress capability is exceeded, the tension member being subjected to a tensile force t, the termination device comprising:
a socket; and
a wedge that fits within the socket with the tension member wrapped around the wedge, the wedge having a clamping surface that includes a length l and is disposed at an angle ϕ, which is measured between a centerline of the wedge and the clamping surface and which relates to the length l in accordance with the formula that defines a minimum of the angle ϕ:
ϕ=tan−1(t/(σc*l*w)). 0. 7. A method for terminating a tension member having a width w and comprised of a plurality of inner load carrying cords and a compressible coating, wherein the compressible coating defines a traction surface for the tension member and has a predetermined maximum compressive stress capability σc, the compressible coating being subject to compressive creep if the predetermined maximum compressive stress capability is exceeded, the method comprising:
feeding the tension member into an aperture of a socket;
wrapping the tension member around a wedge having a clamping surface that includes a length l and is disposed at an angle ϕ, which is measured between a centerline of the wedge and the clamping surface;
feeding the tension member back through the aperture; and applying a tensile force t in the tension member so that the tension member is compressed between the wedge and the socket, wherein the tensile force t is applied in accordance with the formula that defines a minimum of the angle ϕ:
ϕ=tan−1(t/(σc*l*w)). 3. A method according to
positioning the tension member in a back-to-back arrangement;
placing a pair of plates on either side of the tension member;
inserting a plurality of fasteners through the plates;
tightening the fasteners; and
clamping the tension member between the plates in a double overlap arrangement.
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This application is a divisional of application Ser. No. 09/224,045, filed Dec. 31, 1998, now U.S. Pat. No. 6,256,841.
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.
Although conventional 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. Typical techniques to increase the traction forces between the ropes and sheave result in reducing the durability of the ropes, increasing wear or the increasing rope pressure.
Another limitation on the use of steel ropes is the flexibility and fatigue characteristics of steel wire ropes. The minimum diameter of a steel rope is dictated mostly by fatigue requirements and results in a relatively thick rope. The relatively thick cross section of a steel rope reduces its inherent flexibility necessitating a sheave having a relatively large diameter. The larger the sheave diameter, the greater torque required from the machine to drive the elevator system thereby increasing the size and cost of the elevator system.
Another drawback of conventional round ropes is that smaller sheave diameters increase rope pressure shortening the life of the rope. Rope pressure is generated as the rope travels over the sheave and is directly proportional to the tension in the rope and inversely proportional to the sheave diameter D and the rope diameter. 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.
In a typical rope driven elevator installation rope wedge clamps are used for termination purposes. Wedge clamps operate by securing the elevator rope between opposed angled walls of the wedge clamps and a tear drop shaped wedge around which the cable is wound. The wedge acts to cam the rope against the walls of the wedge clamp during tensioning of the ropes. A benefit of this design is that the wedge may have a relatively sharp angle producing a large clamping force. Because the steel ropes have a high compressive strength the large clamping force has no deleterious effects on the rope such as crush or creep.
In attempts to overcome the deficiencies and drawbacks of conventional round steel ropes for use in elevator systems coated tension members, including a relatively flat tension member, has been developed. The flat tension member includes a plurality of individual load carrying cords encased within a common layer of coating. An exemplary tension member of the type contemplated in this application is discussed in further detail in U.S. Ser. No. 09/031,108 filed Feb. 26, 1998 Entitled Tension Member For An Elevator and Continuation-In-Part Application Entitled Tension Member For An Elevator filed Dec. 22, 1998, both of which are entirely incorporated herein by reference.
The coating layer surrounds and/or 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, traction is increased and smaller sheave diameters are possible.
A method of terminating and securing flat tension members involves looping the members over a bar and clamping the end with a pair of plates. The plates are secured by a plurality of fasteners that pass through holes provided in the plates. Another method of terminating flat tension members includes a wedged end fastener wherein a wedge of material is positioned at the end of the tension member and clamped by a pair of plates. In such a configuration one of the plates comprises a wedge shaped cross section cooperating with the wedge of material and the second plate comprises a cross section of uniform thickness. The plates are similarly secured by a plurality of fasteners that pass through holes provided in the plates. A drawback to these types of termination methods is that the tension carrying capability of the termination relies solely on the clamping forces provided by the fasteners. In addition, the wedge type fastener limits the termination point of the member and hampers adjustability.
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 termination device for a tension member having a compressible outer coating has a wedge disposed in a socket having cooperating jaw surfaces. The rope is wrapped around the wedge and inserted with the socket and clamped therein by forces generated by the tension in the member and the cooperation of the wedge and jaw surfaces.
A principal feature of the present invention is the geometry of the wedge, particularly the angle of the wedge, including its length and width. The wedge is sized and the angle is selected to provide sufficient clamping force to resist slippage of the rope without exceeding the compressive stress capability of the tension member. In addition, the wedge comprises a domed top portion to efficiently distribute the tension of the rope across the wedge.
Illustrated in
An embodiment of terminal clamp 30 is illustrated in more detail in
Referring to
Still referring to
An alternative embodiment of termination clamp 30 is shown in
The geometry of wedge 32 is an important factor in producing normal forces 68, 70 and properly retaining tension member 22. The relevant parameters of wedge 32 controlling the normal force Fn are shown with reference to
ϕ=tan−1[T/(σc*L*W)]
In a typical application of the present invention for a tension member having a T of about 2500 N, d ranges from about 60 mm to about 70 mm, L is about 140 mm, ϕ ranges from about 9 degrees to about 10 degrees.
The present invention will now be described with respect to a specific example of the termination clamp 30 shown in
d=2(L tan ϕ)=2(140 tan 20/2))=49.37 mm
The determination of Fn with T equal to 2500 N is as follows:
Fn=T/sin ϕ=2500/sin (20/2)=14,397 N
Since Fn is distributed over the entire area of lead portion 44 the compressive stress σ on the tension member 22 is a function of the area of lead portion, A, clamped between wedge 32 and jaw surface 62, and is calculated as follows:
A=L*W=140*30=4,200 mm2
The compressive stress in tension member 22 is then determined as follows:
σ=Fn/A=14,397/4,200=3.43 MPa
In this particular example, the compressive stress limit of the material is not exceeded and therefore no creep will occur.
The ability of termination clamp 30 to react out T in lead section 44 is important and is a function of Fn and the coefficient of friction (μ) between the tension member 22 and jaw surface 62 and the surface of wedge 32. In the example given, tension member 22 is comprised of a urethane coating and jaw surface 62, as well as wedge 32, is smooth steel and a conservative number for the coefficient friction between the surfaces is about μ=0.25. To properly maintain wedge 32 within socket 34 T must be preferably substantially reacted out within lead section 44 although a remainder may be transferred into wrap section 47. The following relation, from clamping theory, provides the maximum reaction force Fr, or the amount of tension that can be reacted, in the example given for μ=0.25:
Fr=μ*Fn=0.25*14,397=3,599 N
Therefore, recalling that the maximum T in the example given is 2500 N, all of the tension T will be reacted out of tension member 22 in the lead portion 44 and the member will not slip within termination clamp 30.
An alternative embodiment of the present invention aimed at increasing the coefficient of friction between the tension member 22 and the jaw surface 62, 64 and wedge 32 comprises a roughened surface on the jaws and the wedge. In one particular embodiment the surface is roughened by a sandblasting procedure. Sandblasting of the surfaces raises the coefficient of friction to 0.35 or greater. Other methods of increasing the surface friction include etching, machining, knurling and other suitable equivalents. In addition to raising the coefficient of friction the roughened surfaces would form small ridges and valleys. A characteristic of the urethane coating is its tendency to exhibit cold flow under high loading conditions. Under the loading conditions described above the urethane coating cold flows into and around the ridges and valleys, also referred to as locking features, in the wedge and socket and provides for a small but effective mechanical lock. The locking features increase the ability of the termination clamp to resist slippage of tension member 22. It is within the scope of the present invention that the locking features may comprise grooves, striations 83 (
An alternative embodiment for wedge 32 is shown in
Referring now to
As described hereinabove tension clamp 50 comprises a pair of plates 56, 58 each having a tension member groove 52, 54 approximately the thickness of the tension member 22. Bore holes 51 are provided for through passage of fasteners 53. Plates 56, 58 further include leading edges 55 comprising a generous radius to facilitate a smooth transition of lead portion 44 and tail portion 48 from socket 34 into tension clamp 50.
In use, the lead portion 44 is inserted into groove 52 of plate 56 and tail portion 48 into groove 54 of plate 58 and the plates are assembled together with fasteners 53. When the bolts 53 are tightened tension member 22 is clamped within the grooves 52, 54 and are held resistant to slippage by plates 56, 58. In this way the tension member is prevented from moving relative to tension clamp 50.
When optional tension clamp 50 is used in conjunction with termination clamp 30, leading portion 44 and tail portion 48 load share the full tension created by car 14. In this regard, the analysis for determining the clamping performance established herein above is modified to reflect a load sharing in the tension in each of the cables.
While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.
Ericson, Richard J., Baranda, Pedro, Rehmer, Dennis J.
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