Patent Publication Number: US-10308479-B2

Title: Elevator installation

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Entry of International Patent Application Serial Number PCT/EP2014/002637, filed Sep. 29, 2014, which claims priority to German Patent Application No. DE 102013110791.5 filed Sep. 30, 2013, the entire contents of both of which are incorporated herein by reference. 
     FIELD 
     The present disclosure relates to elevator systems that employ counterweights. 
     BACKGROUND 
     A variety of different configurations of elevator systems having at least one elevator car and at least one counterweight are known. The at least one elevator car can be displaced vertically upward and downward in the shaft by means of a cable arrangement or a belt arrangement. The cable arrangement or belt arrangement may be guided over a traction sheave which, together with a drive motor which makes the traction sheave rotate, forms a drive device for the elevator car. In order to compensate for its weight, the elevator car is coupled to a counterweight via the cable arrangement or belt arrangement. 
     If such elevator systems are used in very high buildings, then the cable arrangement or belt arrangement has a very great length. This may result in the cable arrangement or belt arrangement being caused to vibrate for example by movement of the building in which the elevator system is installed. Building movements of this kind can be brought about by wind loading or, for example, also by earthquakes. The vibration results in the cable arrangement or belt arrangement being deflected in the horizontal direction. There is a risk here of a cable portion or belt portion colliding with a component of the elevator system, and so the cable portion or belt portion or also the component of the elevator system might be damaged. 
     In order to limit horizontal deflection of a cable portion or belt portion, WO 92/17396 proposes the use of a limiting member which can be pivoted about a horizontal pivot axis and can be positioned laterally on a cable portion or belt portion in order to limit the horizontal deflection of the same. If the limiting member is positioned laterally alongside a cable portion or a belt portion as the elevator car is travelling upward or downward, then it may be the case that the cable portion or belt portion executes a movement relative to the limiting member and slides along the limiting member. This, in turn, may result in the cable portion or belt portion working the limiting member mechanically. The limiting member therefore has to have a high level of mechanical strength in order to avoid damage. Moreover, it is also possible for the cable portion or belt portion to be damaged if it slides along the limiting member. 
     Therefore, a need exists for elevator systems that prevent damage to limiting members or cable or belt portions in the event a cable or belt portion is deflected horizontally. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic longitudinal-sectional view of an example elevator system. 
         FIG. 2  is a cross-sectional view of the example elevator system taken across line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a schematic view of an example elevator system. 
         FIG. 4  is a schematic view of another example elevator system. 
     
    
    
     DETAILED DESCRIPTION 
     Although certain example methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. 
     Example elevator systems of the present disclosure may generally include a shaft in which at least one elevator car can be displaced vertically upward and downward and is coupled to a counterweight via a cable arrangement or belt arrangement, wherein the cable arrangement or belt arrangement has at least one cable portion or belt portion, of which the horizontal deflection can be limited by at least one limiting member. Those having ordinary skill in the art will understand that the terms ‘cable’ and ‘belt’ may be used interchangeably herein. 
     Furthermore, some example elevator systems include at least one limiting member configured in the form of a limiting roller which is mounted laterally alongside a cable portion or belt portion such that it can be rotated about an axis of rotation. In some cases, the limiting roller can be made to rotate by a controllable rotary drive in dependence on the speed and the movement direction of the cable portion or belt portion, arranged laterally alongside the limiting roller, relative to the axis of rotation of the limiting roller. 
     In order to limit vibration of a cable portion or belt portion, use is made, in the case of the elevator system according to the invention, of at least one limiting roller which is mounted in a rotatable manner and can be made to rotate by a rotary drive. This makes it possible to reduce the speed of the cable portion or belt portion, arranged laterally alongside the limiting roller, relative to the limiting roller when the elevator car is traveling. For this purpose, the controllable rotary drive can make the limiting roller rotate in dependence on the speed and the movement direction of the cable portion or belt portion relative to the axis of rotation of the limiting roller. For example, provision may be made for the circumferential speed of the limiting roller which, in the event of vibration, comes into contact with the cable portion or belt portion arranged laterally alongside the limiting roller to be approximated by the rotary drive to the relative speed of said cable portion or belt portion, wherein the limiting-roller contact region against which the cable portion or belt portion can be positioned during horizontal deflection moves upward or downward in the same direction as the cable portion or belt portion. The cable portion or belt portion and the contact region of the limiting roller thus have the same movement direction. The greater the approximation of the speeds, the lower is the speed at which the cable portion or belt portion moves relative to the contact region of the limiting roller. This reduces the risk of the cable portion or belt portion and/or the limiting roller being damaged. The greater the speed of the cable portion or belt portion relative to the axis of rotation of the limiting roller, the greater is also the circumferential speed of the limiting roller which is made to rotate by the controllable rotary drive. The controllable rotary drive can move the limiting roller in the clockwise direction and counter-clockwise direction. 
     In the case of the elevator system according to the invention, the direction of rotation and the circumferential speed of the limiting roller used for limiting vibration of a cable portion or belt portion arranged laterally alongside the limiting roller can be adapted to the speed and the movement direction of said cable portion or belt portion relative to the axis of rotation of the limiting roller. As a result, if the cable portion or belt portion executes a horizontal deflection, and comes into contact with the outer circumference of the adjacent limiting roller, when the elevator car is traveling, the cable portion or belt portion moves, at most, at low speed relative to the outer circumference of the limiting roller, and therefore neither the limiting roller nor the cable portion or belt portion are badly damaged. 
     It is particularly advantageous if the circumferential speed of the limiting roller corresponds to the speed of the cable portion or belt portion, arranged laterally alongside the limiting roller, relative to the axis of rotation of the limiting roller. In the event of horizontal deflection, the cable portion or belt portion comes into contact with the outer circumference of the limiting roller. If the limiting roller is made to rotate by its rotary drive such that the circumferential speed of the limiting roller is identical to the speed of the cable portion or belt portion relative to the axis of rotation of the limiting roller, then, when the two come into contact, the cable portion or belt portion rolls on the outer circumference of the limiting roller without this resulting in sliding movement and mechanical working of the limiting roller. Damage to the limiting roller and/or to the cable portion or belt portion can thus be reliably prevented. 
     It is advantageous if the rotary drive, which makes the limiting roller rotate, is coupled to an elevator-control apparatus, wherein the elevator-control apparatus can supply the rotary drive with a control signal which is dependent on the speed and the movement direction of the cable portion or belt portion, arranged laterally alongside the limiting roller, relative to the axis of rotation of the limiting roller. The elevator-control apparatus controls the travel of the elevator car and also advantageously determines the speed and the movement direction of a cable portion or belt portion, arranged laterally alongside a limiting roller, relative to the axis of rotation of the limiting roller. On the basis of the relative speed determined, in particular calculated, and of the relative-movement direction determined, in particular calculated, the elevator-control apparatus can supply the rotary drive of the limiting roller with a control signal, which causes the rotary drive to drive the limiting roller to rotate such that the direction of rotation and circumferential speed thereof are adapted to the relative speed, and the direction of the relative movement, of the adjacent cable portion or belt portion. During operation of the elevator system, it is thus possible for the circumferential speed and the direction of rotation of the limiting roller to be changed in accordance with the change in relative speed, and the change in direction of movement, of the adjacent cable portion or belt portion. 
     In the case of an advantageous embodiment of the invention, at least one limiting roller is mounted in a rotatable manner in a predetermined position in the shaft. For example, provision may be made for at least one limiting roller to be arranged in the center of the shaft, as seen in relation to the vertical extent of the shaft. 
     Provision may also be made for the elevator system to have a plurality of limiting rollers distributed uniformly in the shaft in a region between the uppermost stop of the at least one elevator car and the lowermost stop of the at least one elevator car. 
     Provision may also be made for at least one limiting roller to be mounted in a rotatable manner on an elevator car. Such a positioning of at least one limiting roller on an elevator car is advantageous, in particular, when a cable portion or belt portion is guided along said elevator car. In the event of vibration of the cable portion or belt portion, it is possible here for the at least one limiting roller to limit deflection in the direction of the elevator car, and therefore the cable portion or belt portion cannot adversely affect the elevator car even if vibration occurs. 
     It is advantageous if the at least one limiting roller arranged on an elevator car has its circumferential region, which comes into contact with a cable portion or belt portion in the event of lateral deflection, projecting laterally beyond a side wall of the elevator car. Such positioning ensures that, in the case of horizontal deflection, the cable portion or belt portion extending laterally alongside the elevator car can come into contact, at most, with the circumferential region of the limiting roller, but not with the side wall. 
     It is preferable for at least one limiting roller to be mounted in a rotatable manner laterally alongside a cable portion or belt portion which extends in the vertical direction to a counterweight. This cable portion or belt portion may be a suspension-cable or suspension-belt portion which extends vertically upward from the counterweight. As an alternative, or in addition, it may also be a compensating-cable or compensating-belt portion which extends vertically downward from the counterweight. It is particularly advantageous if limiting rollers are mounted in a rotatable manner on mutually opposite sides of the cable portion or belt portion extending to the counterweight. 
     In the case of an advantageous configuration of the invention, at least one elevator car is arranged between two cable portions or belt portions, wherein at least one limiting roller is arranged laterally alongside each of the two cable portions or belt portions. The two cable portions or belt portions may be oriented with point symmetry with respect to one another, as seen in relation to a center axis of the elevator car. By supplying in each case at least one limiting roller in order to limit any lateral deflection of the cable portions or belt portions, it is possible to ensure in a straightforward manner in design terms that the elevator car positioned between the two cable portions or belt portions cannot be adversely affected by the cable portions or belt portions even when the latter are caused to vibrate. 
     Provision may be made, for example, for the elevator car to be suspended on the two cable portions or belt portions. In the case of such a configuration, the two cable portions or belt portions form suspension means, on which the elevator car is retained. For the purpose of suspending the elevator car on the cable portions or belt portions, it is possible for laterally outwardly projecting suspension elements to be retained on the elevator car. The suspension elements used may be, for example, fastening elements which each secure a cable end or belt end on the elevator car. As an alternative, it is also possible to use rotatable or non-rotatable suspension rollers, around which the cable portions or belt portions are guided. Starting from the suspension means, the cable portions or belt portions extend vertically upward and, in the event of vibration, lateral deflection of the cable portions or belt portions can be limited with the aid of limiting rollers. 
     In the case of a particularly preferred configuration of the invention, the elevator system has a first elevator car and a second elevator car, which is arranged beneath the first elevator car, the two elevator cars being displaceable vertically upward and downward separately from one another in the shaft and being coupled to a counterweight in each case via a cable arrangement or belt arrangement, wherein at least one cable arrangement or belt arrangement has two cable portions or belt portions which extend vertically in the shaft, from one of the two elevator cars, along mutually opposite sides of the other elevator car, which is arranged between the two cable portions or belt portions, wherein at least one limiting roller is mounted in a rotatable manner laterally alongside each of the cable portions or belt portions in the shaft and/or on the elevator car arranged between the two cable portions or belt portions. 
     The transporting capacity of the elevator system can be increased by supplying two elevator cars which are arranged one above the other in a shaft and can be displaced vertically upward and downward, separately from one another, along a common track. The two elevator cars are each assigned a drive device with a traction sheave, which can help to drive the respective elevator car. Each of the two elevator cars is assigned a counterweight, to which the elevator car is coupled via a cable arrangement or belt arrangement. 
     Elevator systems having two elevator cars arranged one above the other in a shaft are used, in particular, in very high buildings. As already explained, it is precisely in such buildings that there is a risk of cable portions or belt portions being caused to vibrate, which results in the cable portions or belt portions being deflected horizontally. In the case of two elevator cars coupled to a counterweight in each case via a cable arrangement or a belt arrangement being arranged one above the other, at least one of the two elevator cars is advantageously positioned between two cable portions or belt portions and, in order to avoid damage to the elevator car and/or to the cable portions or belt portions running along mutually opposite sides of the elevator car, each of the cable portions or belt portions is assigned at least one limiting roller which limits lateral deflection of the cable portion or belt portion and is mounted in a rotatable manner in the shaft or also on the elevator car. 
     It is particularly advantageous if at least two limiting rollers, each positioned alongside a cable portion or belt portion, are mounted in a rotatable manner on the two elevator cars. 
     Provision may be made for in each case two limiting rollers to be mounted in a rotatable manner on the upper side and on the underside of the elevator car arranged between the two cable portions or belt portions, said limiting rollers being arranged laterally alongside a cable portion or belt portion extending from the other of the two elevator cars. Supplying limiting rollers both on the upper side and on the underside of the elevator car arranged between the two cable portions or belt portions ensures that the cable portions or belt portions cannot come into contact with the elevator car even in the event of very pronounced vibration. 
     As already mentioned, the second elevator car is arranged beneath the first elevator car. It is advantageous if the second elevator car is suspended on two suspension-cable or suspension-belt portions which extend vertically upward from the second elevator car and between which the first elevator car is arranged, wherein each of the two suspension-cable or suspension-belt portions has arranged alongside it at least one limiting roller which is mounted in a rotatable manner on the first elevator car. By means of the limiting rollers mounted in a rotatable manner on the first elevator car, it is possible to limit the extent to which the suspension-cable or suspension-belt portions extending vertically upward from the second elevator car are deflected horizontally in the direction of the first elevator car. 
     Limiting rollers which are arranged on those sides of the suspension-cable or suspension-belt portions which are directed away from the two elevator cars are advantageously mounted in a rotatable manner in the shaft in each case alongside a suspension-cable or suspension-belt portion. By means of the limiting rollers mounted in a rotatable manner in the shaft, it is thus possible to limit horizontal deflection of the suspension-cable or suspension-belt portions in the directions away from the elevator cars and, by means of the limiting rollers mounted in a rotatable manner on the first elevator car, it is possible to limit deflection of the suspension-cable or suspension-belt portions in the direction of the first elevator car. 
     It is advantageous if rotatably mounted limiting rollers are arranged on mutually opposite sides of at least one suspension-cable or suspension-belt portion. 
     In the case of an advantageous configuration of the invention, the limiting rollers mounted in a rotatable manner on the first elevator car are arranged on the upper side thereof. 
     As an alternative, provision may be made for the limiting rollers mounted in a rotatable manner on the first elevator car to be arranged on the underside thereof. 
     It is particularly advantageous if limiting rollers which limit horizontal deflection of the suspension-cable or suspension-belt portions extending vertically upward from the second elevator car are arranged both on the upper side and on the underside of the first elevator car. 
     Provision may also be made, in addition to the limiting rollers mounted in a rotatable manner on the first elevator car, for rotatably mounted limiting rollers which limit horizontal deflection of the suspension-cable or suspension-belt portions extending vertically upward from the second elevator car also to be arranged on the second elevator car. 
     In particular in the case of very high buildings, and correspondingly very long suspension-cable or suspension-belt arrangements, it is advantageous if the weight of each suspension-cable or suspension-belt arrangement is compensated for by a compensating-cable or compensating-belt arrangement. In the case of such a configuration, each elevator car is coupled to its counterweight via a suspension-cable or suspension-belt arrangement and, in addition, via a compensating-cable or compensating-belt arrangement. The suspension-cable or suspension-belt arrangement is guided over a traction sheave arranged above the two elevator cars and the compensating-cable or compensating-belt arrangement is guided over a deflecting device arranged beneath the two elevator cars. 
     In the case of an advantageous configuration of the invention, the first elevator car is coupled to a counterweight via two compensating-cable or compensating-belt portions, wherein the compensating-cable or compensating-belt portions extend vertically downward from the first elevator car and the second elevator car is arranged between the two compensating-cable or compensating-belt portions, and wherein each of the compensating-cable or compensating-belt portions has arranged alongside it at least one limiting roller which is mounted in a rotatable manner on the second elevator car. In the case of such a configuration, at least two limiting rollers which are mounted in a rotatable manner on the second elevator car are used for the purpose of limiting horizontal deflection of the compensating-cable or compensating-belt portions between which the second elevator car is arranged. 
     It is advantageous if limiting rollers which are positioned on those sides of the compensating-cable or compensating-belt portions which are directed away from the two elevator cars are arranged in the shaft in each case alongside a compensating-cable or compensating-belt portion. By means of the limiting rollers arranged in the shaft, it is thus possible to limit lateral deflection of the compensating-cable or compensating-belt portions in the directions away from the elevator cars and, by means of the limiting rollers mounted in a rotatable manner on the second elevator car, it is possible to limit horizontal deflection of the compensating-cable or compensating-belt portions in the direction of the second elevator car. 
     It is advantageous if rotatably mounted limiting rollers are arranged on mutually opposite sides of at least one compensating-cable or compensating-belt portion. 
     In the case of an advantageous configuration of the invention, the limiting rollers mounted in a rotatable manner on the second elevator car and limiting lateral deflection of a compensating-cable or compensating-belt portion are mounted in a rotatable manner on the upper side of the second elevator car. 
     As an alternative, provision may be made for limiting rollers to be mounted in a rotatable manner on the underside of the second elevator car, for the purpose of limiting lateral deflection of the compensating-cable or compensating-belt portions guided along the second elevator car. 
     It is particularly advantageous if limiting rollers which are arranged a lateral deflection of the compensating-cable or compensating-belt portions extending vertically downward from the first elevator car are mounted in a rotatable manner both on the upper side and on the underside of the second elevator car. 
     Provision may also be made, in addition to the limiting rollers mounted in a rotatable manner on the second elevator car, for rotatably mounted limiting rollers which limit horizontal deflection of the compensating-cable or compensating-belt portions extending vertically downward from the first elevator car also to be arranged on the first elevator car. 
     In particular also in the case of elevator systems having two elevator cars which can be displaced one above the other and separately from one another, it is advantageous if at least one limiting roller which extends vertically downward or upward to a counterweight is mounted in a rotatable manner in the shaft laterally alongside a cable portion or belt portion, as has already been explained above. 
       FIGS. 1 and 2  illustrate, schematically, a first advantageous embodiment of an elevator system according to the invention, which is designated as a whole by the reference sign  10 . The elevator system  10  comprises a shaft  12  with a rear wall  14 , a front wall  16  and a first side wall  18  and a second side wall  20 . The shaft  12  extends in the vertical direction from a shaft pit  22 , which is limited vertically downward by a shaft floor  24 , up to a shaft head  26 , which is limited vertically upward by a shaft ceiling  28 . 
     An elevator car  30  can be displaced vertically upward and downward in the shaft  12  along guide rails which are known per se and therefore, to give a better overview, are not illustrated in the drawing. For the purpose of driving the elevator car  30 , use is made of a drive device having a traction sheave  32 , which can be made to rotate by a drive motor (not illustrated in the drawing). The drive motor of the traction sheave  32  is connected to an elevator-control apparatus  34 , which controls the elevator system  10 . 
     The elevator car  30  is coupled to a counterweight  38  via a suspension-cable arrangement  36 . Instead of a suspension-cable arrangement  36 , it would also be possible, as an alternative, to use a suspension-belt arrangement. 
     The suspension-cable arrangement  36  is guided over the traction sheave  32  and comprises a first suspension-cable portion  40  and a second suspension-cable portion  42 , on which the elevator car  30  is suspended. The elevator car  30  is positioned between the two suspension-cable portions  40 ,  42 , wherein the two suspension-cable portions  40 ,  42  extend along mutually opposite sides of the elevator car. Starting from a first cable end  44 , which is secured on the shaft ceiling  28 , the first suspension-cable portion  40  extends vertically downward to a first suspension roller  46 , which is mounted in a rotatable manner, facing toward the second side wall  20  of the shaft  12 , on the underside  48  of the first elevator car  30 . A second suspension roller  50  is mounted in a rotatable manner, facing toward the first side wall  18  of the shaft  12 , on the underside  48  of the elevator car  30 . A connecting portion  52  of the suspension-cable arrangement  36  runs in the horizontal direction essentially diagonally along the underside  48  and connects the first suspension-cable portion  40  to the second suspension-cable portion  42 , which follows the second suspension roller  50  in the vertically upward direction and extends to the traction sheave  32 . From the traction sheave  32 , a third suspension-cable portion  54  runs to a deflecting roller  56 , which is mounted in a rotatable manner on an upper side of the counterweight  38 . Starting from the first deflecting roller  56 , a fourth suspension-cable portion  58  extends vertically upward to a second cable end  60 , which is secured on the shaft ceiling  28 . 
     For the purpose of limiting horizontal deflection of the first suspension-cable portion  40  in the direction of the second side wall  20 , a first limiting roller  62  is mounted such that it can be rotated about a first axis of rotation  64  approximately centrally, as seen in the vertical direction, in the shaft. The first limiting roller  62  is arranged on that side of the first suspension-cable portion  40  which is directed toward the second side wall  20 , and therefore horizontal deflection of the first suspension-cable portion  40  in the direction of the second side wall  20  can be limited by means of the first limiting roller  62 . 
     In order also to limit lateral deflection of the first suspension-cable portion  40  in the direction away from the second side wall  20 , a second limiting roller  70  is mounted such that it can be rotated about an axis of rotation  72  on the upper side  66  of the elevator car  30 , and laterally alongside the first suspension-cable portion  40 . The first suspension-cable portion  40 , which is fixed on the shaft ceiling  28 , does not execute any vertical movement relative to the first limiting roller  62 . In the event of vibration, the first suspension-cable portion  40  can thus come into contact with the first limiting roller, but does not slide along the first limiting roller, and therefore the risk of damage to the first limiting roller  62  by the first suspension-cable portion  40  is low. In contrast to this, the first suspension-cable portion  40  moves relative to the second limiting roller  70 , which is mounted in a rotatable manner on the elevator car  30 , when the elevator car  30  is traveling upward or downward. In order to avoid the first suspension-cable portion sliding along the second limiting roller  70 , and damaging the second limiting roller  70 , in the event of horizontal deflection, the second limiting roller  70  is assigned a rotary drive in the form of a controllable electric motor  74 , with the aid of which the second limiting roller  70  can be made to rotate about the axis of rotation  72 . The electric motor  74  is connected to the elevator-control apparatus  34  via a control line which, to give a better overview, is not illustrated in the drawing. As explained in yet more detail hereinbelow the circumferential speed and the direction of rotation of the second limiting roller  70  can be adapted to the speed and the movement direction of the first suspension-cable portion  40  by means of the electric motor  74 . 
     A third limiting roller  78  is mounted such that it can be rotated about an axis of rotation  80  on the upper side of the elevator car  30 , on the side directed away from the second limiting roller  70 . The third limiting roller  78  is assigned a controllable rotary drive in the form of an electric motor  82 , with the aid of which the third limiting roller  78  can be made to rotate about the third axis of rotation  80 . The third electric motor  82  is connected to the elevator-control apparatus  34  via a control line (not illustrated in the drawing). 
     Level with the first limiting roller  62 , a fourth limiting roller  86  is mounted such that it can be rotated about an axis of rotation  88  on the first side wall  18  of the shaft  12 . The fourth limiting roller  86  is assigned a controllable rotary drive in the form of an electric motor  90 , with the aid of which the fourth limiting roller  86  can be made to rotate about the fourth axis of rotation  88 . The fourth electric motor  90  is likewise connected to the elevator-control apparatus  34  via a control line. 
     By means of the first limiting roller  62  and of the fourth limiting roller  86 , it is possible to limit horizontal deflection of the two suspension-cable portions  40 ,  42  in the direction away from the elevator car  30  and, by means of the second limiting roller  70  and of the third limiting roller  78 , it is possible to limit horizontal deflection of the two suspension-cable portions  40 ,  42  in the direction of the elevator car  30 . 
     When the elevator car  30  moves in the vertical direction, the first suspension-cable portion  40  moves relative to the axis of rotation  72  of the second limiting roller  70  and the second suspension-cable portion  42  moves relative to the axis of rotation  80  of the third limiting roller  78  and also relative to the axis of rotation  88  of the fourth limiting roller  86 . In order to avoid the first suspension-cable portion  40  sliding along the outer circumference of the second limiting roller  70 , and this resulting in mechanical working of the second limiting roller  70  or of the first suspension-cable portion  40 , during horizontal deflection, the circumferential speed and the direction of rotation of the second limiting roller  70  can be adapted by the controllable electric motor  74  to the relative speed and movement direction of the first suspension-cable portion  40  relative to the axis of rotation  72  of the second limiting roller  70 . Consequently, the outer circumference of the second limiting roller  70  rolls on the first suspension-cable portion  40  without this resulting in any relative movement between the first suspension-cable portion  40  and the outer circumference of the second limiting roller  70 . For the purpose of controlling the circumferential speed in dependence on the relative speed and movement direction of the first suspension-cable portion  40 , the electric motor  74  is supplied with an appropriate control signal by the elevator-control apparatus  34 . 
     When the elevator car  30  moves, the first suspension-cable portion  40  does not execute any vertical movement relative to the first limiting roller  62 . The first limiting roller  62  thus does not require any rotary drive to adapt its circumferential speed and direction of rotation to the speed and movement direction of the first suspension-cable portion  40  relative to the axis of rotation  64  of the first limiting roller  62 . 
     However, adaptation of the circumferential speed and of the direction of rotation to the relative speed and movement direction of the second suspension-cable portion  42  takes place for the third limiting roller  78  and for the fourth limiting roller  86 . For this purpose, the circumferential speeds and direction of rotations of the third limiting roller  78  and of the fourth limiting roller  86  can be adapted to the relative speed and the movement direction of the second suspension-cable portion  42  when the elevator car  30  moves relative to the axis of rotation  80  of the third limiting roller  78  and/or relative to the axis of rotation  88  of the fourth limiting roller  86 . For this purpose, the electric motors  82  and  90  of the third limiting roller  78  and of the fourth limiting roller  86  are supplied with appropriate control signals by the elevator-control apparatus  34 . Consequently, when the elevator car  30  moves, the second suspension-cable portion  42  rolls on the outer circumference of the third limiting roller  78  and also on the outer circumference of the fourth limiting roller  86 . Damage to the third limiting roller  78  and to the fourth limiting roller  86  can thus be reliably prevented. 
     The arrangement of the limiting rollers  62 ,  70 ,  78  and  86  is clear, in particular, from  FIG. 2 , in which, to give a better overview, the counterweight  38  is not illustrated. 
     Further limiting rollers  92 ,  93 ,  94  and  95  are mounted in a rotatable manner in the shaft  12  on either side of the third and fourth suspension-cable portions  54 ,  58 . Like the limiting rollers  70 ,  78 ,  86  explained above, it is also possible for the limiting rollers  92 - 95  to be made to rotate in each case by a controllable electric motor such that the direction of rotation and circumferential speed thereof corresponds to the movement direction and the relative speed of the suspension-cable portions  54  and/or  58 . Horizontal deflection of the suspension-cable portions  54 ,  58 , which extend in the vertical direction to the counterweight  38 , can thus be limited without the suspension-cable portions  54 ,  58  or the limiting rollers  92 - 95  being damaged. 
     A second advantageous embodiment of an elevator system according to the invention is illustrated schematically in  FIG. 3  and designated as a whole by the reference sign  100 . The elevator system  100  has a shaft  102  in which a first elevator car  104  and a second elevator car  106 , which is arranged beneath the first elevator car  104 , can be displaced vertically upward and downward, separately from one another, along common guide rails, which, to give a better overview, are not illustrated in the drawing. 
     The first elevator car  104  is coupled to a first counterweight  110  via a first suspension-cable arrangement  108 , wherein the first suspension-cable arrangement  108  is guided over a first traction sheave  112 , which can be made to rotate by a drive motor (not illustrated in the drawing) for the purpose of displacing the first elevator car  104 . The first traction sheave  112  is controlled by means of an elevator-control apparatus  114 . 
     The second elevator car  106  is coupled to a second counterweight  118  via a second suspension-cable arrangement  116 . The second suspension-cable arrangement  116  is guided over a second traction sheave  120 , which can be made to rotate by a drive motor (not illustrated in the drawing). The second traction sheave  120  is likewise controlled by means of the elevator-control apparatus  114 . 
     In a manner corresponding to the suspension-cable arrangement  36  explained above with reference to  FIGS. 1 and 2 , it is also the case that the second suspension-cable arrangement  116  of the elevator system  10  has a first suspension-cable portion  122  and a second suspension-cable portion  124 . The first suspension-cable portion  122  extends in the vertical direction from a first cable end  128 , which is secured on the ceiling  126  of the shaft  102 , to a first suspension roller  130 , which is arranged on the underside of the second elevator car  106 , and the second suspension-cable portion  124  extends in the vertical direction from a second suspension roller  132 , which is arranged on the underside of the second elevator car  106 , to the second traction sheave  120 . 
     The first elevator car  104  is arranged between the first suspension-cable portion  122  and the second suspension-cable portion  124 . In order to restrict vertical deflection of the first suspension-cable portion  122  and of the second suspension-cable portion  124 , the elevator system  100  illustrated in  FIG. 3  makes use, in a manner corresponding to the elevator system  10  illustrated schematically in  FIGS. 1 and 2 , of a first limiting roller  134 , a second limiting roller  136 , a third limiting roller  138  and a fourth limiting roller  140 , wherein the second limiting roller  136 , the third limiting roller  138  and the fourth limiting roller  140  can be made to rotate in each case by an associated rotary drive in the form of a controllable electric motor  142 ,  144  and  146  in dependence on the relative speed and the movement direction of the first suspension-cable portion  122  and the second suspension-cable portion  124  in relation to the axis of rotation of the respective limiting rollers  134 ,  136  and  138 ,  140 . For this purpose, the electric motors  142 ,  144 ,  146  are connected to the elevator-control apparatus  114  via control lines (not illustrated in  FIG. 3 ). The elevator-control apparatus  114  supplies the electric motors  142 ,  144  and  146  with control signals which are dependent on the speed and the movement direction of the first suspension-cable portion  122  relative to the axis of rotation of the second limiting roller  136  and of the second suspension-cable portion  124  relative to the axes of rotation of the third limiting roller  138  and of the fourth limiting roller  140 . As already explained, this can ensure that the first suspension-cable portion  122  can roll on the outer circumference of the second limiting roller  136 , and that the second suspension-cable portion  124  can roll on the outer circumference of the third limiting roller  138  and of the fourth limiting roller  140 . 
     In addition to the limiting rollers  134 ,  136 ,  138  and  140 , the elevator system  100  makes use of five further limiting rollers  148 ,  150 ,  152 ,  154  and  156 . In each case two limiting rollers  148 ,  150  are mounted in a rotatable manner on an upper side of the first elevator car  104 , and two further limiting rollers  152 ,  154  are mounted in a rotatable manner on the underside of the first elevator car  104 . A further limiting roller  156  is mounted in a rotatable manner in the shaft  102  laterally alongside a third suspension-cable portion  158 , which, in a manner corresponding to the third suspension-cable portion  54  explained above with reference to  FIG. 1 , extends between the second traction sheave  120  and a deflecting roller  160 , which is mounted in a rotatable manner on the upper side of the second counterweight  180 . 
     The limiting rollers  148 ,  150 ,  152 ,  154  and  156  can be made to rotate in each case by a controllable rotary drive in the form of an electric motor  162 ,  164 ,  166 ,  168  and  170 , wherein the circumferential speed and the direction of rotation of the limiting rollers  148 ,  150 ,  152 ,  154  and  156  corresponds in each case to the relative speed and the movement direction of the suspension-cable portion  122 ,  124  and  158 , which comes into contact with the respective limiting roller in the event of horizontal deflection, relative to the axis of rotation of the respective limiting roller. For this purpose, it is also the case that the electric motors  162 ,  164 ,  166 ,  168  and  170  are connected to the elevator-control apparatus  114  via control lines (not illustrated in  FIG. 3 ), said elevator-control apparatus supplying the aforementioned electric motors with control signals in dependence on the relative speed and movement direction of the suspension-cable portions  122 ,  124  and  158 . 
     In the case of the elevator system  100 , horizontal deflection of the suspension-cable portions  122 ,  124  and  158  can thus be limited by means of the limiting rollers  134 ,  136 ,  138 ,  140 ,  148 ,  150 ,  152 ,  154  and  156 , which are arranged laterally alongside the suspension-cable portions  122 ,  124  and  158 , without the risk of the limiting rollers and/or suspension-cable portions being damaged. 
       FIG. 4  illustrates schematically a third advantageous embodiment of an elevator system according to the invention, which is designated as a whole by the reference sign  180 . In a manner corresponding to the elevator system  100  illustrated above with reference to  FIG. 3 , it is also the case that the elevator system  180 , which is illustrated in  FIG. 4 , has a shaft  182  in which a first elevator car  184  and a second elevator car  186 , which is arranged beneath the first elevator car  184 , can be displaced vertically upward and downward separately from one another. The first elevator car  184  is coupled to a first counterweight  190  via a first suspension-cable arrangement  188 , wherein the first suspension-cable arrangement  188  is guided over a first traction sheave  192 , and the second elevator car  186  is coupled to a second counterweight  196  via a second suspension-cable arrangement  194 , wherein the second suspension-cable arrangement  194  is guided over a second traction sheave  198 . 
     In a manner corresponding to the second elevator car  106  explained above with reference to  FIG. 3 , it is also the case that the second elevator car  186  of the elevator system  180  is suspended on a first suspension-cable portion  200  and a second suspension-cable portion  202  and the first elevator car  184  assumes a position between the first suspension-cable portion  200  and the second suspension-cable portion  202 . 
     In order to limit any horizontal deflection of the first suspension-cable portion  200 , a first limiting roller  204  is mounted such that it can be rotated about an axis of rotation  205  approximately centrally, as seen in the vertical direction, in the shaft  182 , on that side of the first suspension-cable portion  200  which is directed away from the elevator cars  184 ,  186 , and a second limiting roller  206  is mounted such that it can be rotated about an axis of rotation  208  on the underside of the first elevator car  184 , wherein the second limiting roller  206  is assigned a controllable rotary drive in the form of an electric motor  210 , with the aid of which the second limiting roller  206  can be made to rotate in dependence on the speed and the movement direction of the first suspension-cable portion  200  relative to the axis of rotation  208  of the second limiting roller  206 . The electric motor  210  is connected to an elevator-control apparatus  212  of the elevator system  180  via a control line (not illustrated in  FIG. 4 ). 
     In order to limit any horizontal deflection of the second suspension-cable portion  202 , a third limiting roller  214  is mounted such that it can be rotated about an axis of rotation  216  approximately centrally, as seen in the vertical direction, in the shaft, and said third limiting roller can be made to rotate by an electric motor  218  in dependence on the speed and the movement direction of the second suspension-cable arrangement  194  relative to the axis of rotation  216 , and therefore the circumferential speed and the direction of rotation of the third limiting roller  214  are identical to the speed and the movement direction of the second suspension-cable portion  202  relative to the axis of rotation  216  of the third limiting roller  214 . The third limiting roller  214  is arranged on that side of the second suspension-cable portion  202  which is directed away from the two elevator cars  184 ,  186 . 
     A fourth limiting roller  220  is mounted such that it can be rotated about an axis of rotation  222  on the underside of the first elevator car  194 , laterally alongside the second suspension-cable portion  202 , wherein the fourth limiting roller  220  can be made to rotate by an associated electric motor  224  in dependence on the relative speed and the movement direction of the second suspension-cable portion  202  relative to the axis of rotation  222  of the fourth limiting roller  220 . The electric motor  224 , like the electric motor  218 , is connected to the elevator-control apparatus  212  via a control line (not illustrated in  FIG. 4 ). 
     In order for it to be possible to compensate for the weight of the first suspension-cable arrangement  188 , the first elevator car  184  is also coupled to the first counterweight  190  via a first compensating-cable arrangement  226 . The compensating-cable arrangement  226  is secured on the underside of the first counterweight  190  by way of a first cable end  228  and by way of a second cable end  230  and is guided over a first deflecting roller  232  and a second deflecting roller  234 , which are mounted in a rotatable manner on an upper side of the first elevator car  184 . A first compensating-cable portion  236  here extends vertically downward from the first deflecting roller  232  to a cable-deflecting device  238 , which is arranged in a pit  240  of the shaft  182 , and a second compensating-cable portion  242  extends vertically downward from the second deflecting roller  234  to the cable-deflecting device  238 . 
     The second elevator car  186 , which is arranged beneath the first elevator car  184 , is positioned between the first compensating-cable portion  236  and the second compensating-cable portion  242 . In order to limit horizontal deflection of the first compensating-cable portion  236 , a fifth limiting roller  250  is mounted such that it can be rotated about an axis of rotation  252  approximately centrally, as seen in the vertical direction, in the shaft  182 , wherein the fifth limiting roller  250  is assigned a controllable rotary drive in the form of an electric motor  254 . The electric motor  254  is connected to the elevator-control apparatus  212  via a control line (not illustrated in  FIG. 4 ) and makes the fifth limiting roller  250  rotate such that the circumferential speed and direction of rotation of the fifth limiting roller  250  correspond to the relative speed and the movement direction of the first compensating-cable portion  236  relative to the axis of rotation  252  of the fifth limiting roller  250 . 
     A sixth limiting roller  256  is mounted such that it can be rotated about an axis of rotation  258  on the upper side of the second elevator car  186 . The sixth limiting roller  256  can be made to rotate by an electric motor  260  such that the circumferential speed and direction of rotation of the sixth limiting roller  256  correspond to the relative speed and movement direction of the first compensating-cable portion  236  relative to the axis of rotation  258 . 
     In order for it to be possible to limit horizontal deflection of the second compensating-cable portion  242 , a seventh limiting roller  262  is mounted such that it can be rotated about an axis of rotation  264  approximately centrally, as seen in the vertical direction, in the shaft  182 , on that side of the second compensating-cable portion  242  which is directed away from the two elevator cars  184 ,  186 , and said seventh limiting roller can be made to rotate by an electric motor  266 , which is connected to the elevator-control apparatus  212  via a control line (not illustrated in  FIG. 4 ), wherein the circumferential speed and the direction of rotation of the seventh limiting roller  262  correspond to the relative speed and movement direction of the second compensating-cable portion  252  relative to the axis of rotation  264  of the seventh limiting roller  262 . 
     An eighth limiting roller  268  is mounted such that it can be rotated about an axis of rotation  270  on the upper side of the second elevator car  186 , laterally alongside the second compensating-cable portion  242 , and said eighth limiting roller can be made to rotate by an electric motor  272 . The electric motor  272  is connected to the elevator-control apparatus  212  via a control line (not illustrated in  FIG. 4 ) and makes it possible for the eighth limiting roller  268  to move in rotation such that the circumferential speed and direction of rotation of the eighth limiting roller  268  are identical to the relative speed and the movement direction of the second compensating-cable portion  242  relative to the axis of rotation  270  of the eighth limiting roller  268 . 
     Horizontal deflection of the two suspension-cable portions  200 ,  202  can thus be limited by means of the limiting rollers  204 ,  206 ,  214  and  220 , and horizontal deflection of the two compensating-cable portions  236 ,  242  can be limited by means of the limiting rollers  250 ,  256 ,  262  and  268 . The limiting rollers are driven to rotate in each case such that the circumferential speed and the direction of rotation of the limiting rollers correspond to the relative speed and the movement direction of the respective suspension-cable or compensating-cable portion relative to the axis of rotation of the limiting roller when the elevator car is traveling. This ensures that the suspension-cable and compensating-cable portions roll on the circumferences of the limiting rollers without damaging these or themselves. 
     Further limiting rollers which, to give a better overview, are not illustrated in  FIG. 4  are mounted in a rotatable manner in the shaft  182  in the region beneath the first counterweight  190  and the second counterweight  196  in order to limit horizontal deflection of the compensating cables extending in the vertical direction from the cable-deflecting device  238  to the counterweights  190 ,  196 . Furthermore, it is also possible for limiting rollers which can help to limit horizontal deflection of the suspension cables extending in the vertical direction to the counterweights  190 ,  196  to be mounted in a rotatable manner in the shaft, above the two counterweights  190 ,  196 . The limiting rollers which are mounted in a rotatable manner in the shaft both above and beneath the counterweights  190 ,  196  can be made to rotate in each case by a controllable electric motor such that their direction of rotation and their circumferential speed correspond to the movement direction and the relative speed of the respective suspension cable or compensating cable with which the respective limiting roller comes into contact during horizontal deflection.