Patent Publication Number: US-2007111588-A1

Title: Support Means with Connection Able to Accept Shearing Force for Connecting Several Cables

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a support means for use in an elevator installation with several cables extending at a spacing from one another and a cable casing.  
      Running cables are an important, highly loaded machine element in conveying technology, particularly in the case of elevators, in crane construction and in mining. The loading of driven cables, as used in, for example, elevator construction, is particularly complex.  
      In the case of conventional elevator installations, elevator car and counterweight are connected together by way of several steel strand cables. The cables run over a drive pulley driven by a drive motor. The drive moment is imposed under friction couple on the respective cable section lying on the drive pulley over the looping angle. In that case the cable experiences tension, bending, compression and torsional stresses. The relative motions arising due to the bending over the cable pulley cause friction within the cable structure, which can have a negative effect on cable wear. Depending on a respective cable construction, bending radius, groove profile and cable safety factor the primary and secondary stresses which arise have a negative influence on the cable state.  
      Apart from strength requirements, there is the further requirement in the case of elevator installations for, for reasons of energy, smallest possible masses. High-strength synthetic fiber cables, for example of aromatic polyamides, especially aramides, fulfill these requirements better than steel cables.  
      Cables made of aramide fibers have, for the same cross-section and same load-bearing capability, by comparison with conventional steel cables only a quarter to a fifth of the specific cable weight. By contrast to steel, however, aramide fiber has a substantially lower transverse strength in relation to longitudinal load-bearing capability.  
      Consequently, in order to expose the aramide fibers to the smallest possible transverse stresses when running over the drive pulley a parallelly stranded aramide fiber strand cable suitable as a drive cable is proposed in, for example, European Patent Application EP 0 672 781 A1. The aramide cable known therefrom offers very satisfactory values with respect to service life, high abrasion strength and alternate bending strength; however, in unfavorable circumstances the possibility exists with parallelly stranded aramide cables that partial cable unraveling phenomena occur which permanently disturb the original cable structure in its balance. These twisting phenomena and the changes in cable structure can be avoided with, for example, a synthetic fiber cable according to European Patent Application EP 1 061 172 A2. For this purpose the synthetic fiber cable comprises two parallelly extending cables which are connected together by way of a cable casing. The synthetic fiber cable according to EP 1 061 172 A2 achieves a longitudinal strength substantially through the characteristics of the two cables extending in parallel. The cable casing, thereagainst, prevents twisting phenomena and changes in the cable structure. Moreover, the cable casing serves as insulation (protective effect) and it has a high coefficient of friction. A weak point can be, depending on the respective field of application and use, the web of such a synthetic fiber cable according to EP 1 061 172 A2.  
      Support means with two and more cables have disadvantages if they are so moved during running around a drive pulley that the individual cables run on tracks with different radius. Due to the radius differences the cables are moved by the traction of the drive pulley at different speed. The web part of the cable casing is thereby exposed to a shearing stress. Due to the shearing action the web region of the cable casing can be damaged, particularly when shearing forces occurring dynamically are concerned.  
     SUMMARY OF THE INVENTION  
      The present invention has an object of further improving the known support means, which comprise two or more cables, in order inter alia to avoid web fracture. This applies particularly to support means comprising synthetic fiber cables.  
      The invention is based on recognition that the stated problems do not gain the upper hand if the web region is stiffened. Thus, the direct effects of shearing forces can indeed be prevented, but in this case the more rapidly circulating cable drags along the other cable and slip occurs which causes increased abrasion.  
    
    
     DESCRIPTION OF THE DRAWINGS  
      The above, as well as other, advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:  
       FIG. 1A  is a perspective illustration of a first support means according to the present invention with two cables;  
       FIG. 1B  is a plan view of the support means according to  FIG. 1A ;  
       FIG. 2  is a plan view of a second embodiment support means according to the present invention with two cables and rectangular webs;  
       FIG. 3  is a plan view of a third embodiment support means according to the present invention with two cables and parallelogram-shaped webs with obliquely extending edges; and  
       FIG. 4  is a plan view of a fourth embodiment support means according to the present invention with two cables and convexly shaped webs. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Constructional elements which are the same or have the same effect are provided in all figures with the same reference numerals even if they are not of identical construction in details. The figures are not to scale.  
      A first support means  10  for use in an elevator installation is shown in  FIG. 1A  and  FIG. 1B . The support means  10  comprises at least two cables  11 . 1  and  11 . 2 . These cables  11 . 1  and  11 . 2  comprise, for example, a plurality of synthetic fiber strands  12  designed for acceptance of force in a longitudinal direction L. The cables  11 . 1  and  11 . 2  are arranged parallel to one another along the longitudinal direction L of the support means  10  at a spacing Al (center-to-center). The cables  11 . 1 ,  11 . 2  are fixed relative to one another, to be secure against twisting, by a cable casing  13 . The cable casing  13  forms a transition region  14 , which extends parallel to the longitudinal direction L of the support means  10 , between the two cables,  11 . 1 ,  11 . 2 .  
      According to the present invention the transition region  14  of the cable casing  13 , which lies between the cables  11 . 1 ,  11 . 2 , is provided with openings  14 . 2  and webs  14 . 1 . The webs  14 . 1  are formed so that they make possible a relative movement of the cables  11 . 1 ,  11 . 2  with respect to one another in the longitudinal direction L.  
      It can be seen on the basis of  FIGS. 1A and 1B  how this transition region  14  is designed in the case of the first embodiment. The cable casing  13  is a common cable casing which encloses the first cable  11 . 1  and the second cable  11 . 2 . The cable casing  13  extends over into the transition region  14  to the webs  14 . 1 , which webs ultimately serve as the sole connections between the two adjacent cables  11 . 1  and  11 . 2 .  
      According to the present invention at least two cables are thus connected together, but not by a rigid connection. The connection between the adjacent cables  11 . 1 ,  11 . 2  of the support means  10  according to the present invention is created by way of the webs  14 . 1 , which webs on the one hand make possible transmission of torsional moments from one cable  11 . 1  to the adjacent cable  11 . 2 , but on the other hand enable displacement of the cables  11 . 1 ,  11 . 2  relative to one another in the longitudinal direction L of the support means  10 .  
      It is important that the webs  14 . 1  are so designed that they make possible the relative displacement at least in certain sections of the support means  10  without, however, breaking or tearing.  
      The first embodiment, which is shown in  FIGS. 1A and 1B , of the support means  10  has openings  14 . 2  which are straight on the two longitudinal sides (parallel to the longitudinal axis L) and outwardly convex in the end regions. The webs  14 . 1  in the plan view shown in  FIG. 1B  are correspondingly dumbbell-shaped. The webs  14 . 1  thus have, as seen in longitudinal direction, boundaries which extend into the web concavely.  
      The term “relative displacement of the adjacent cables” includes, according to the present invention, two cases:  
      (1) the two cables  11 . 1 ,  11 . 2  can be uniformly displaced relative to one another over their entire length (with the same stretching of the cables); and  
      (2) one of the cables  11 . 1  and  11 . 2  can be stretched more than the other, wherein, during the stretching, relative displacements between individual length sections of the respective cables arise (the amount of the relative displacement in that case depends on the length position on the cable).  
      Further embodiments of the support means according to the present invention each with the two cables  11 . 1 ,  11 . 2  are shown in  FIGS. 2, 3  and  4 . These support means are, as also the support means  10  shown in  FIGS. 1A, 1B , designed for use in an elevator installation. The support means comprise the two cables  11 . 1 ,  11 . 2 , wherein each of the cables includes several of the strands  12 . The cables  11 . 1 ,  11 . 2  are designed for acceptance of force in the longitudinal direction L, wherein the cables  11 . 1 ,  11 . 2  are arranged along the longitudinal direction L of the support means at the spacing A 1  from one another and are connected by means of the common cable casing  13 . The cable casing  13  forms the transition region  14  between the two cables  11 . 1 ,  11 . 2 . The transition region of the cable casing  13 , which lies between the cables  11 . 1 ,  11 . 2 , is provided with openings and webs (similar to the openings  14 . 2  and the webs  14 . 1 ), wherein also in the case of the embodiments shown in  FIGS. 2, 3  and  4  the webs are designed so that they enable a relative movement of the cable  11 . 1 ,  11 . 2  with respect to one another in the longitudinal direction L.  
      The embodiments shown in  FIGS. 2, 3  and  4  differ substantially only by the form of the webs and by the dimensioning of the webs or the openings.  
      The second embodiment of the support means, which is shown in  FIG. 2 , is a support means  10   a  having a plurality of openings  14 . 2   a  which are straight on two longitudinal sides (parallel to the longitudinal axis L) and which are straight in end regions, i.e. the openings  14 . 2  are substantially rectangular in the plan view shown in  FIG. 2 . Correspondingly, a plurality of webs  14 . 1   a  in the plan view shown in  FIG. 2  are rectangular or square.  
      The third embodiment of the support means, which is shown in  FIG. 3 , is a support means  10   b  having a plurality of openings  14 . 2   b  which extend rectilinearly on two longitudinal sides (parallel to the longitudinal axis L) and which extend at an inclination in end regions, i.e. the openings  14 . 2   b  are approximately parallelogram-shaped in the plan view shown in  FIG. 3 . Correspondingly, a plurality of webs  14 . 1   b  in the plan view shown in  FIG. 3  are also lozenge-shaped with obliquely extending edges.  
      The fourth embodiment of the support means, which is shown in  FIG. 4 , is a support means  10   c  having openings  14 . 2   c  which are straight on two longitudinal sides (parallel to the longitudinal axis L) and which are concave in end regions. Correspondingly, a plurality of webs  14 . 1   c  in the plan view shown in  FIG. 4  are curved outwardly at both sides, i.e. convex.  
      The described principle can also be transferred to an assembly of three and more cables.  
      In the preferred embodiments of the present invention the strands  12  of the cables are laid so that at least two of the cables of the support means  10 ,  10   a ,  10   b ,  10   c build up, under torsional stress, (mutually compensating) intrinsic torsional moments of opposite sense.  
      In the examples shown in the figures the strands  12  of each of these cables are respectively laid parallelly (with the same rotational sense), whilst the strands of adjacent cables  11 . 1  and  11 . 2  are laid with opposite rotational sense.  
      The webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c  are an integral component of the casing  13 . They can in this case be made in a single production step (by extrusion or vulcanization according to the respective material) together with the casing  13 .  
      The webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c  can be either produced during production of the casing  13  together therewith or they can be formed in a subsequent step (for example, by punching).  
      An optimization parameter is the elasticity of the webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c . Through optimization of the elasticity, relative displacements of the cables are allowed and disturbing shear stresses in the transition region  14  between adjacent cables  11 . 1 ,  11 . 2  can be reduced.  
      Advantageously the length ratios between the webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c  and the openings  14 . 2 ,  14 . 2   a ,  14 . 2   b ,  14 . 2   c  are so selected that the webs of resilient material function to a first approximation in an articulated manner under shearing forces in the longitudinal direction (L) of the cables, i.e. the webs can accept substantially only forces in a transverse direction with respect to the cables  11 . 1  and  11 . 2 . Such webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c  constructed in an articulated manner thus cannot accept substantial forces in the longitudinal direction (L) when there are small relative displacements of the cables  11 . 1  and  11 . 2  and thus avoid, in the case of occurrence of different cable speeds of the adjacent cables  11 . 1  and  11 . 2  such as arise with running surface differences of the drive pulleys, large shearing forces in the transition region of the cable casing  13 , which can lead to material failure in the said region. These shearing forces lead to shear stresses which lie in the low double-figure percentage range of the shear strength of the cable casing material.  
      A suitable material for production of the cable casing  13  is polyurethane. Two commercially available polyurethane synthetic materials suitable for use as the cable casing  13  are Elastollan 1185 and Elastollan 1180, which slightly differ. Elastollan is a registered trade mark of the BASF.  
      Examples of relative displacements of the cables  11 . 1 ,  11 . 2  are presented in concrete terms in the following.  
      Elastollan 1185 has a modulus of elasticity of 20 MPa, a shear modulus of 9 MPa and a Poisson&#39;s ratio of 0.11. If now the cables  11 . 1 ,  11 . 2  displace relative to one another by a longitudinal displacement s =0.8 millimeters there results in the case of a cable spacing “t” of 2.3 millimeters, a web length “LI” of 3.0 millimeters, a web thickness “d” of 3.4 millimeters and the use of Elastollan 1185, a shearing force of 32.1 N and a shear stress of 3.15 MPa, which the web absorbs. This example shows that the webs absorb only small shearing forces and the shear stress resulting therefrom lies far below the shear strength of the above-mentioned polyurethane. The shear stresses reach approximately 15% of the shear strength.  
      Shearing forces of 24.3 N and shear stresses of 2.4 MPa result under the same conditions as above for an Elastollan 1180 with a shear modulus of 6.8 MPa. The shear stresses reach approximately 11% of the shear strength.  
      Further examples for longitudinal displacement “s” of the cables  11 . 1 ,  11 . 2  of 0.7 millimeters and 0.6 millimeters in the case of use of Elastollan 1185 yield shear stresses of 2.7 MPa and 2.4 MPa. These shear stresses respectively correspond with 13% and 11% of the shear strength.  
      Elastomers have a yield elongation of more than 100% which can amount to up to 800%. However, it is to be noted that elongations of 25% and more are to be avoided, since otherwise irreversible deformations can quite easily occur. The longitudinal displacements “s” of 0.6, 0.7 and 0.8 millimeters of the cables  11 . 1 ,  11 . 2  shown by way of example in the foregoing correspond with strains of 20% and less. It follows therefrom that relative displacements of the cables  11 . 1 ,  11 . 2  in the sub-millimeter range do not lead to impermissible material loads of the webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c.    
      Moreover, it is possible to equip the individual webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c  with a mechanical reinforcement.  
      The use of the support means  10 ,  10   a ,  10   b ,  10   c  with synthetic fiber cables is particularly preferred. Metallic, synthetic and/or organic strands  12 , or a combination of the said materials, is or are particularly preferred.  
      The cables  11 . 1 ,  11 . 2  are preferably produced by two-stage or multi-stage twisting of the strands  12 . The cables  11 . 1 ,  11 . 2  comprising three layers  12 . 2 ,  12 . 3 ,  12 . 4  with strands and a central strand  12 . 1  are shown in  FIG. 1A . However, this is only an example for the construction of the cables  11 . 1 ,  11 . 2 .  
      Cable yarns of aramide fibers, for example, can be twisted together in the cables  11 . 1 ,  11 . 2 .  
      As can be seen in the figures, the entire outer circumference of the cables  11 . 1 ,  11 . 2  is enclosed by the common cable casing  13  of synthetic material. The cable casing  13  can comprise synthetic and/or organic materials. The following materials are particularly suitable as cable casings: rubber, polyurethane, polyolefine, polyvinylchloride or polyamide. The respective resiliently deformable synthetic material is preferably sprayed or extruded on the cables  11 . 1 ,  11 . 2  and subsequently compacted thereon. The cable casing material thereby penetrates from outside into all interstices between the strands  12  at the outer circumference and fills up these. The thus-created coupling of the cable casing  13  to the strands  12  is so strong that only small relative movements arise between the strands  12  of the cables  11 . 1 ,  11 . 2  and the cable casing  13 .  
      According to a further embodiment short fiber pieces (for examples glass fibers, aramide fibers or the like) or a woven mat can be embedded in the web  14  and serves or serve as reinforcement.  
      The support means  10 ,  10   a ,  10   b ,  10   c  shown in the figures are particularly suitable for drive by a cable pulley, wherein the force transmission between the cable pulley and the support means takes place substantially by friction couple.  
      The two or more cables  11 . 1 ,  11 . 2  are, according to the present invention, so connected together that the torsional moment of one cable  11 . 1  is transmitted to the other cable  11 . 2  and conversely. The torsional moments thereby compensate one another. In the ideal case the total torsional moment of the support means  10 ,  10   a ,  10   b ,  10   c  in the case of an even-numbered number of cables and with symmetrical construction is equal to zero. By contrast to the known support means, the cables of the support means according to the present invention are not connected together by a single transition region extending over the entire length of the support means, but by a number of the webs  14 . 1 ,  14 . 1   a ,  14 . 1   b ,  14 . 1   c  (plurality of transverse connections). These transverse connections are relatively stiff relative to forces transverse to the longitudinal direction L of the support means, but are designed to be sufficiently narrow with respect to the longitudinal direction of the support means. By comparison with conventional support means according to the state of the art cited above, the transverse connections in the support means according to the present invention are significantly less stiff in the longitudinal direction. The transverse connections of the cables are thereby relatively easily resiliently deformable by shear forces in the longitudinal direction L of the support means  10 ,  10   a ,  10   b ,  10   c  (by contrast to the state of the art). The two cables  11 . 1 ,  11 . 2  of the support means can accordingly easily be displaced relative to one another in the longitudinal direction L by shear forces acting in the longitudinal direction. Equally, the two cables  11 . 1 ,  11 . 2  can accept stretchings of different magnitude in the longitudinal direction L without damage of the transverse connections.  
      The forms of embodiment according to the present invention make it possible to avoid fractures or weakenings in the transition region  14  in that shearing movements are converted into longitudinal displacements parallel to the longitudinal axis L. Damage of the transition region  14  and at the same time abrasion of conventional support means with two or more cables can thereby be reduced.  
      The double, triple or multiple cable according to the present invention can without problems provide compensation for running radius differences at drive pulleys when the cables of the support means move at a drive pulley along circular paths of different radius and accordingly at different speed at the circumference of the drive pulley.  
      In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.