Abstract:
A lifting apparatus for lifting and lowering a load comprises, in a known manner, a lifting drum and a drive, by which the lifting drum can be set in rotation in both directions. Serving as the pulling mechanisms are bands which are secured by one end to the lifting drum and at the other end carry a holding device for the load. At least two bands can be wound up on the lifting drum, by rotation of the latter, with accurate tracking and so as to lie one above the other, in such a way that all the turns of the bands lie one above the other. This lifting apparatus combines a high carrying capacity, high precision in the guidance of the bands and a high level of operating safety.

Description:
SUMMARY OF INVENTION  
       [0001]     The invention relates to a lifting apparatus for lifting and lowering a load, having 
    a) a lifting drum;     b) a drive, by which the lifting drum can be set in rotation in both directions;     c) at least two bands, serving as pulling means, which are secured by one end to the lifting drum and at the other end carry a holding device for the load;     d) the bands being able to be wound up on the lifting drum, by rotation of the latter, in such a way that one turn lies above the other.    
 
         [0006]     A wide variety of configurations of lifting apparatuses employing a lifting drum and at least one flexible pulling means which can be wound up on this drum are known. Ropes, chains or bands, in particular, are used as the pulling means. Bands have the advantage that they can be wound up on the lifting drum in a particularly well-defined manner and have a relatively high carrying capacity, while nevertheless remaining sufficiently flexible. For this reason, lifting apparatuses which employ bands as the pulling means, with which the present invention is also concerned, are enjoying increasing popularity.  
         [0007]     A plurality of load-carrying bands are generally employed in cases where the carrying capacity of the lifting apparatus is to be increased or loads with large dimensions are to be lifted and lowered. In such lifting apparatuses known from the market, the different bands were wound up on the lifting drum one beside the other, i.e. in different axial regions. However, this gives rise to geometrical problems with the band guidance, in particular where there are a large number of bands or the space is confined.  
         [0008]     The object of the present invention is to configure a lifting apparatus of the type mentioned at the outset in such a way that, while maintaining precise guidance of the bands, a large number of bands, suited to the requirements, can be employed without much space being required for their guidance.  
         [0009]     This object is achieved according to the invention in that 
    e) at least two bands can be wound up on the lifting drum with accurate tracking and so as to lie one above the other.    
 
         [0011]     According to the invention, the plurality of bands are thus no longer wound up one beside the other in axially different regions, but one above the other in the same axial region of the lifting drum. It is now no longer turns of one and the same band that lie directly one above the other, but turns of different bands. The winding-up behaviour of these bands lying one above the other can be controlled very well. Moreover, they can be guided in a relatively confined space. Each of the bands lying one above the other can be dimensioned in such a way that, in an emergency when another band breaks, it can take over the share of the load which has hitherto been carried by this other band and in this way emergency operation of the lifting apparatus is possible. This contributes to increased operating safety of the lifting apparatus.  
         [0012]     Winding a plurality of bands on the lifting drum one above the other in the manner according to the invention gives rise to the problem that, on unwinding the bands from the lifting drum, at a certain angular rotation different lengths of the bands are unwound. This results from the fact that the turns of the bands, which are unwound simultaneously, lie on different radii. A configuration of the invention is therefore recommended in which the lower ends of the bands are connected to a holding device for the load, which is configured as a compensating device for the varying lengths, on winding up and unwinding, of the unwound parts of the bands lying one above the other on the lifting drum. This compensating device makes it possible for the lower ends of the bands lying one above the other to move at slightly different speeds on unwinding or winding up, without losing the uniform load distribution to the different bands.  
         [0013]     By way of example, it is possible for two bands to be able to be wound up on the lifting drum with accurate tracking and so as to lie one above the other. In this case, the holding device can comprise a rocker element which connects the lower ends of the two bands to one another, the rocker element having, between the points at which the force is introduced by the bands, a fastening device for the load. The different vertical movements of the lower ends of the bands lying one above the other is offset by a pivoting of the rocker element.  
         [0014]     In this case, the lower ends of the bands are expediently secured in clamping pieces articulated in opposite regions of the rocker element.  
         [0015]     If three bands are to be able to be wound up on the lifting drum with accurate tracking and so as to lie one above the other, the following construction is possible: the lower ends of the two outer bands are connected to one another, the holding device comprising a deflection roller which is carried by the middle band and around which the connection between the two outer bands is guided. The vertical position of the holding device is in this case determined substantially by the middle band, while the vertical positions of the lower ends of the two outer bands are displaced, on unwinding and winding up, in opposite directions relative to the lower end of the middle band. As a result of the non-positive connection between the lower ends of the outer bands, the same stress is always present in these bands. The length of the middle band must be dimensioned in such a way that this band too carries substantially the same share of the load. This design presupposes, however, that at least the two outer bands have the same thickness.  
         [0016]     The lower ends of the two outer bands can, in principle, be connected to one another in one piece, with the result that the two outer bands are formed by a single band laid around the deflection roller. A more favourable construction, however, is that in which the lower ends of the two outer bands are connected to one another by a piece of rope or chain which is guided around the deflection roller. It is thereby possible to use smaller-diameter and thus space-saving deflection rollers.  
         [0017]     It is also possible for four bands to be able to be wound up on the lifting drum with accurate tracking and so as to lie one above the other. In this case, a design can be employed in which the lower ends of the first pair of adjacent bands and the lower ends of the second pair of adjacent bands are connected to one another, the holding device comprising: 
    a) a rocker element;     b) a first deflection roller, around which the connection of the lower ends of the first pair of bands is guided and which is mounted in an end region of the rocker element;     c) a second deflection roller, around which the connection of the lower ends of the second pair of bands is guided and which is mounted in the opposite end region of the rocker element; and     d) the rocker element, at a point lying between the points at which the deflection rollers are mounted, having a fastening device for the load.    
 
         [0022]     In this design, the two deflection rollers perform a vertical movement which corresponds to an average of the vertical movement of the two bands with which these deflection rollers are associated. Through the rocker element, in turn, a further averaging of the vertical positions of the two deflection rollers takes place.  
         [0023]     In this latter design too, it is recommended for the reasons already mentioned above that the connections of the lower ends of the two pairs of bands are pieces of rope or chain.  
         [0024]     The winding-up and unwinding of the bands lying one above the other involves a sliding movement of these bands relative to one another. It is therefore favourable if the bands are provided with a friction-reducing coating on at least one side, which coating may be a graphite or Teflon coating or the like.  
         [0025]     As a result of the fact that the ends of the bands lying one above the other are fastened to the circumferential surface of the lifting drum, a step is formed which has to be overcome by the radially inner band after the first turn. In order to avoid bending of the band at this point, it is advantageous if at least one spacer element, on which the first turn of the radially innermost band can come to bear before reaching the step formed by the ends of the bands, is provided on the circumferential surface of the lifting drum.  
         [0026]     Preferably, the bands consist of metal, in particular of steel. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0027]     Exemplary embodiments of the invention are explained in more detail below with reference to the drawing, in which:  
         [0028]      FIG. 1  shows a section through the lifting drum and two load-carrying bands of a lifting apparatus;  
         [0029]      FIG. 2  shows a detail enlargement from  FIG. 1 ;  
         [0030]      FIG. 3  shows, in section, a holding device used in lifting apparatuses employing three bands; and  
         [0031]      FIG. 4  shows, in section, a holding device used in lifting apparatuses employing four bands. 
     
    
     DETAILED DESCRIPTION  
       [0032]     Reference is made first of all to  FIG. 1 , which can be understood as a highly schematic illustration of a simple lifting apparatus. The lifting apparatus, identified as a whole by the reference symbol  1 , comprises as the main component a lifting drum  2  which is rotatably fitted in two bearing blocks  4  (only one indicated in the drawing) fixed on a mounting plate  3 . The lifting drum  2  can be rotated in both directions of rotation by a drive motor (not illustrated) which is likewise mounted on the mounting plate  3 .  
         [0033]     The mounting plate  3  is placed at a certain height above the room floor, for example by means of a steel structure (not illustrated).  
         [0034]     To lift and lower the load, two steel bands  5   a ,  5   b  are used as the pulling means, which bands can be wound up on the lifting drum  2  with accurate tracking and so as to lie one above the other in a plurality of turns likewise lying one above the other, as can be seen from  FIGS. 1 and 2 . This means that following one another radially from the inside outwards on the lateral surface of the lifting drum  2  are first of all a turn of the steel band  5   a  on the left in  FIG. 1 , then a turn of the steel band  5   b  on the right in  FIG. 1  and then, in accordance with the position of the load to be lifted or lowered, further turns alternately of the steel band  5   a  and of the steel band  5   b.    
         [0035]     As can be seen in particular from  FIG. 2 , the ends  6   a ,  6   b  of the two steel bands  5   a ,  5   b  are suitably secured to the lateral surface of the lifting drum  2 , for example by adhesive bonding, clamping, welding or else simply by the friction produced by turns of the two steel bands  5   a ,  5   b  lying thereabove. In the latter case, the steel bands  5   a ,  5   b  must of course not be unwound from the lifting drum  2  down to the last turn in normal operation.  
         [0036]     The ends  6   a ,  6   b  of the two steel bands  5   a ,  5   b  form a step for the first turn of the steel band  5   a  on the left in  FIG. 1 , which step has to be overcome by the steel band  5   a  and the height of which is equal to the sum of the thicknesses of the two steel bands  5   a  and  5   b . This results in an empty space  7  between the first turn of the steel band  5   a  and the lateral surface of the lifting drum  2 . In order to prevent the first turn of the steel band  5   a  and hence, to a certain extent, also the further turns, lying thereabove, of both steel bands  5   a ,  5   b  from being pressed into the clearance  7  and thereby bent at the step formed by the ends  6   a ,  6   b , a total of three spacer elements  8   a ,  8   b  and  8   c  in the form of metal sheets  8   a ,  8   b  and  8   c  curved in the shape of circular arcs are arranged in this empty space  7 . Each of these metal sheets  8   a ,  8   b  and  8   c  has a constant thickness. The thickness of the metal sheets  8   a ,  8   b ,  8   c  increases, however, in the clockwise direction towards the step formed by the ends  6   a ,  6   b . Generally, the direction in which the thickness of the spacer elements  8   a ,  8   b ,  8   c  is to increase, is opposite that direction in which the lifting drum  2  rotates on lifting the load.  
         [0037]     The spacer elements  8   a ,  8   b ,  8   c  thereby form bearing surfaces for the first turn of the steel band  5   a , preventing this turn from “caving in” too deeply, radially inwards. It is thus not absolutely necessary for the thickness of the spacer elements  8   a ,  8   b ,  8   c  to increase continuously in the stated direction, so as to exactly fill up the empty space  7  formed geometrically. Nor do the spacer elements  8   a ,  8   b ,  8   c  have to butt against one another. They can, seen in the circumferential direction, also be at a distance, which is bridged by the steel band  5   a . The number of spacer elements  8   a ,  8   b ,  8   c  used can vary depending on the circumstances. The result, however, is that the first turn of the steel band  5   a  and hence also the turns, lying thereabove, of both steel bands  5   a ,  5   b  undergo no bending or only insignificant bending at the step formed by the ends  6   a ,  6   b , so that no appreciable alternating loading of the steel bands  5   a ,  5   b  occurs at this point.  
         [0038]     Clamped to the lower ends of each of the steel bands  5   a ,  5   b  is a clamping piece  9   a ,  9   b . The lower regions of the two clamping pieces  9   a ,  9   b  are each articulated with the aid of a bearing pin  10   a ,  10   b  at opposite end regions of a rocker element  11 . The rocker element  11  has in the central region a bore  12 , to which the load (not illustrated) can be attached. The rocker element  11  thereby forms with the clamping pieces  9   a ,  9   b  a holding device  50  for the load.  
         [0039]     The operation of the lifting apparatus  1  described is as follows:  
         [0040]     On lowering a load attached to the rocker element  11 , the lifting drum  2  is rotated in the clockwise direction in  FIGS. 1 and 2 , whereby the two steel bands  5   a ,  5   b  unwind from the lifting drum  2 . Since the steel band  5   b  has been wound up on the lifting drum  2  on a larger radius than the steel band  5   a , at a certain angular rotation of the lifting drum  2  a longer piece of the steel band  5   b  is unwound therefrom than of the steel band  5   a . This difference in length of the two steel bands  5   a ,  5   b  is compensated for by a corresponding tilting of the rocker element  11  about the axis defined by the bore  12 . The stresses within the steel bands  5   a ,  5   b  remain substantially equal in this case, so that the load is uniformly distributed to the two steel bands  5   a ,  5   b.    
         [0041]     In order to reduce the mutual friction as they are wound up on and unwound from the lifting drum  2 , the two steel bands  5   a ,  5   b  are provided with a low-friction coating or intermediate layer, at least on a side which can come to bear on an adjacent steel band  5   a ,  5   b  on winding up. This may be a graphite coating or a Teflon band or the like.  
         [0042]     In the exemplary embodiment described above with reference to  FIGS. 1 and 2 , two steel bands  5   a ,  5   b  have been used to carry the load. If even greater loads are to be lifted and lowered, it may be necessary to increase the number of steel bands to be wound one above the other. Since it is obvious how the relationships on the lifting drum  2  would appear in such a case, a separate illustration of this has been dispensed with. What is interesting in these cases is how the respective lower ends of the steel bands are connected to one another.  
         [0043]     An exemplary embodiment of a holding device  150  which can be employed with three steel bands  105   a ,  105   b  and  105   c  is illustrated in  FIG. 3 . The lower ends of these steel bands  105   a ,  105   b ,  105   c  are again clamped in clamping pieces  109   a ,  109   b ,  109   c . In addition, the two ends of a piece of rope  120 , guided over a deflection roller  121 , are secured in the two outer clamping pieces  109   a ,  109   c  in the manner illustrated in  FIG. 3 . The deflection roller  121  is rotatably mounted in the lower end region of the middle clamping piece  109   b  by means of a bearing journal  122 . The load (not illustrated) is attached to the middle clamping piece  109   b  or to the bearing journal  122 .  
         [0044]     On lifting and lowering the load, its position is determined by the position of the clamping piece  109   b  clamped to the lower end of the middle steel band  105   b . The differences in length which result on unwinding the two lateral steel bands  105   a ,  105   c  are compensated for by the clamping pieces  109   a ,  109   c  attached to their lower ends moving in opposite directions upwards and downwards, the stress present in them being transmitted via the rope  120 . A uniform distribution of the load to all three steel bands  105   a ,  105   b ,  105   c  can thereby be achieved. However, this presupposes that at least the two outer steel bands  105   a ,  105   c  have the same thickness.  
         [0045]     Finally,  FIG. 4  shows how the lower ends of four load-carrying steel bands  205   a ,  205   b ,  205   c  and  205   d  can be connected to one another by a holding device  250 , in order to be able to compensate for the different movements of the lower ends of the steel bands  205   a  to  205   d  while uniformly distributing the load. The holding device  250  illustrated in  FIG. 4  constitutes in a way a combination of the designs described above with reference to  FIGS. 1 and 3 : The lower ends of the steel bands  205   a  to  205   d  are each again clamped in a clamping piece  209   a ,  209   b ,  209   c  and  209   d . Once again, the opposite ends of a piece of rope  220   a , guided over a first deflection roller  221   a , are secured in the adjacent clamping pieces  209   a ,  209   b  associated with the steel bands  205   a ,  205   b . In a corresponding manner, the opposite ends of a second piece of rope  220   b , guided over a second deflection roller  221   b , are clamped to the adjacent clamping pieces  209   c ,  209   d  associated with the steel bands  205   c ,  205   d . The two deflection rollers  221   a ,  221   b  are each rotatably mounted with the aid of a bearing journal  222   a ,  222   b  in the opposite ends of a rocker element  211 .  
         [0046]     In the middle between the two journals  222   a ,  222   b , the rocker element  211  once again has a bore  212 , to which the load (not illustrated) can be attached and which forms the axis of rotation for the tilting of the rocker element  211 .  
         [0047]     The difference in length which arises on unwinding or winding up the adjacent steel bands  205   a ,  205   b  can be compensated for with the aid of the deflection roller  221   a . Correspondingly, the difference in length which results between the steel bands  205   c ,  205   d  can be compensated for by the deflection roller  221   b , while each time ensuring the same stress in the steel bands  205   a ,  205   b  and  205   c ,  205   d  connected via the pieces of rope  220   a ,  220   b , respectively. Differences between the average changes in length of the band pair  205   a ,  205   b , on the one hand, and the band pair  205   c ,  205   d , on the other hand, are compensated for by tilting the rocker element  211  about the axis defined by the bore  212 .