Abstract:
A frequency converter device is integrated inside a cable roller, in such a manner that at least one socket is supplied at special frequency. The socket does not rotate when the cable is wound or unwound on the drum. Furthermore, optimal cooling is created and the frequency converter device is made of at least one frequency converter enabling a special frequency to be provided.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a cable roller according to the preamble of claim  1 . 
   2. Description of the Related Art 
   On building sites, for compacting concrete internal vibrators are often used, the asynchronous motors of which have to be supplied with a special voltage and a special frequency. If, for example, an asynchronous motor provided in the internal vibrator and having a connected flyweight is to reach a rotational speed of 12,000 rpm, then in the case of a double-pole machine an excitation frequency of 200 Hz is required. From the public electricity supply, however, only a frequency of 50 Hz is available. 
   This is why in the past frequency converters were used, which were mostly supplied with three-phase alternating current and owing to their heavy weight were very difficult to handle. Soon, by virtue of the provision of corresponding power electronics with suitable semiconductors it became possible to miniaturize the frequency converter and thereby reduce its weight from e.g. 60 kg to 4 kg. Such a lightweight frequency converter was however still connected between the terminal and a cable drum, which was necessary for bridging larger distances. Moving the terminal, e.g. the internal vibrator, to various work sites therefore also entailed moving the frequency converter and, in addition, the cable drum. 
   From DE 197 22 107 C1 a cable roller is known, in which a frequency converter is integrated, with the result that the cable roller and the frequency converter may be moved as a unit. 
     FIG. 1  shows such an arrangement with a power cable  23 , which is wound on a drum  22 , wherein the drum  22  is carried by a rack  25 . Integrated in the drum  22  is a frequency converter  24 , which supplies at least one socket-outlet  21  with a special electric frequency. Connected to the socket-outlet  21  is a known internal vibrator  20  with an asynchronous motor. Such a combination of cable drum and frequency converter however has the drawback that during take-up or pay-out of the cable the socket-outlets  21  co-rotate with the drum. Consequently, the feeder cable for the internal vibrator  20  may become twisted. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   The underlying object of the invention is to indicate a cable roller having a frequency converter device, with which the handling properties of a construction site appliance in connection with the cable roller/frequency converter device combination are improved and, in particular, the cable take-up system is optimized. 
   The object is achieved according to the invention in the manner defined in claim  1 . Advantageous developments of the invention are evident from the sub-claims. 
   The combining of frequency converter device and cable roller is effected according to the invention in that the frequency converter device is provided in a substantially stationary manner on the frame of the cable roller. In said case, the frame carries the frequency converter device, the frequency converter device may however conversely carry the frame. One advantage of this is the much lower inert mass of the drum, this facilitating take-up or pay-out of the power cable. 
   On the cable roller at least one socket-outlet supplied by the frequency converter device is provided. The electrical connection between the frequency converter device and the power cable is effected by means of at least two slipring devices. The advantage of this electrical connection is that during take-up and/or pay-out of the power cable at least one of the socket-outlets may be substantially stationary, i.e. the socket-outlet does not co-rotate, thereby resulting in improved handling of the equipment plugged in at the cable roller because this equipment no longer has to be unplugged during take-up or pay-out of the cable to prevent twisting of the feeder cable. 
   As the frequency converter device may comprise a plurality of frequency converters, the socket-outlets and hence construction site equipment are suppliable with different special frequencies. 
   It is also advantageous when components, which the various frequency converters comprise, may be combined in the frequency converter device. This means that a plurality of frequency converters may comprise the same components or subassemblies. This constructional option saves space and may be supplemented in that, depending on the style of construction, the drum, on which the power cable is wound, surrounds the frequency converter device comprising one or more frequency converters and forms at least part of a housing of the frequency converter device, or conversely the frequency converter device surrounds the drum and hence forms part of a housing of the drum. 
   For better protection or for improved cooling, the frequency converter device or the drum may in said case be surrounded by an additional housing wall, which is situated between the frequency converter device and the drum, wherein air for cooling purposes is situated in an interspace between the housing wall and the frequency converter device or the drum. 
   It is advantageous to combine the frequency converter device in such a way with the drum that the best possible cooling of the system may be achieved. The cooling may in said case be effected by purposefully providing air slits or cooling bodies on the frame or on the frequency converter device or even on the drum. A further possibility is to integrate fans or special cooling liquids in the cable roller. 
   As a special form of construction of the electrical connection between frequency converter device and power cable, a coupling of at least two inductors or of at least one capacitor is also conceivable. This provides possible ways of circumventing any wear phenomena at the slipring device. 
   Take-up and pay-out of the power cable is usually effected manually. In a particularly advantageous form of construction of the invention, take-up of the cable is effected automatically by rotation of the drum. For this purpose, the known principle of cable take-up in vacuum cleaners may be used. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail below by way of examples and with the aid of the accompanying drawings. The drawings show: 
       FIG. 1  a known arrangement comprising a cable roller with integrated frequency converter and a connected internal vibrator; 
       FIG. 2  a sectional side view of a first form of construction of the cable roller according to the invention; 
       FIG. 3  a sectional side view of a second form of construction of the cable roller according to the invention; 
       FIG. 4  a front view in section of a third form of construction of the cable roller similar to  FIG. 3  having a frequency converter device, which comprises two frequency converters; 
       FIG. 5  a front view in section of a fourth form of construction of the cable roller similar to  FIG. 3  having a frequency converter device, which comprises a plurality of frequency converters; 
       FIG. 6  a side view of a fifth form of construction of the cable roller according to the invention; 
       FIG. 7  a detail A from the side view of  FIG. 3  and  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  shows a sectional side view of a first form of construction of the cable roller according to the invention, having a frequency converter device  2  connected in a substantially stationary manner to a frame  1 . A drum  5  is disposed around the frequency converter device  2  and mounted rotatably about an axis  9 . Wound on the drum  5  is a power cable  3 , which is electrically connected to the frequency converter device  2  by at least two slipring devices  6 . 
   In this embodiment, the drum  5  may form at least part of the housing of the frequency converter device  2 . In said case, the frequency converter device  2  is protectively surrounded by the drum  5 . It is however also conceivable, as is correspondingly illustrated in  FIG. 2 , for the frequency converter device  2  to be surrounded by an independent housing, wherein air is situated between the housing and the drum  5  in order to improve the cooling of the frequency converter device  2 . 
   The connection to the power supply is effected by means of a power plug  4  provided on the end of the power cable  3 . The slipring devices  6 , by which the electrical connection is established between the frequency converter device  2  and the power cable  3 , are seated on the axis of rotation  9 . It is however also conceivable for the slipring devices  6  to be connected in a fixed manner to the frequency converter device  2  and for the axis of rotation  9  to rotate centrically in the slipring devices  6 . The frequency converter device  2  supplies the socket-outlets  7 , which are fastened to the frame  1 , with at least one special frequency, i.e. socket-outlets supplying different special frequencies are also conceivable. 
     FIG. 3  shows the side view of a second form of construction of the cable roller according to the invention having the frequency converter device  2  connected in a substantially stationary manner to the frame  1 . In this embodiment, the frequency converter device  2  forms at least part of the housing of the cable roller. The frequency converter device  2  surrounds the drum  5 , on which is wound the power cable  3 , which is run to the outside through a cable gland  8  that penetrates the frequency converter device  2 . 
   The connection to the power supply is again effected by means of the power plug  4 , The drum  5  is seated on the axis of rotation  9  and freely rotatable about said axis of rotation  9 . Depending on the form of construction of the cable roller, the cable  3  may be taken up by the drum  5  automatically, e.g. in accordance with the known principle of cable take-up in vacuum cleaners. The, in principle, known mechanism required for this purpose is not shown in  FIG. 3 . The connection between the frequency converter device  2  and the cable  3  is again effected by means of a non-illustrated double slipring device. For the socket-outlets  7  and the connection between the power cable  3  and the frequency converter device  2 , the same applies as was stated with regard to  FIG. 2 . 
     FIG. 4  shows in section the front view of a third form of construction of the cable roller similar to  FIG. 3 . The intention here is to make it clear that the frequency converter device  2  may comprise two frequency converters  2   a ,  2   b , which supply different special frequencies. 
     FIG. 5  shows in section a front view of a fourth form of construction of the cable roller corresponding to  FIG. 3 . In this case, however, a plurality of frequency converters  2   a ,  2   b ,  2   c ,  2   d  are arranged in the shape of a ring. 
     FIG. 6  shows the side view of a fifth form of construction of the cable roller according to the invention having a frequency converter device  2 , which is connected in a substantially stationary manner to the frame  1  but in this case, as a base plate, carries the frame  1  and the remainder of the cable roller. The drum  5  is again mounted rotatably on the axis of rotation  9 . The axis of rotation  9  is connected in a fixed manner to the frame  1 . For the socket-outlets  7  and the connection between power cable  3  and frequency converter device  2 , the same applies as was described in connection with  FIG. 2 . 
     FIG. 7  shows a variant of the form of construction according to  FIG. 3 . According to  FIG. 7 , two slipring devices  6  are provided, via which the electric current may be transferred from the power cable  3  wound on the drum  5  to the frequency converter device  2  and finally to the socket-outlets  7 . The slipring devices  6 , which are arrangeable at various points, are used to transfer current from a rotating part (in  FIG. 7 : drum  5  with power cable  3 ) to a stationary part (frequency converter device  2  or/and frame  1 ). 
   As an alternative to the slipring devices, the electric current may be transferred instead by means of suitably disposed inductors or even with the aid of a capacitor arrangement. This depends, however, upon the power rating.