Abstract:
A construction kit for a spring-driven cable drum includes a pre-assembled drum core, the housing of which constitutes a winding surface for the cable and containing at least one spiral spring and at least one spring anchor hub. The pre-assembled drum core is provided with an axle channel passing right through it but no axle. The spring anchor hub is maintained to all intents and purposes coaxial with this axle channel by the spiral springs. The construction kit further includes a separate axle which can be inserted from either side into the axle channel of the pre-assembled drum core, insertion of the axle into the axle channel establishing a form-fit rotary coupling between the spring anchor hub and the axle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of International Application No. PCT/EP2004/050496 filed on Apr. 9, 2004, and European Patent Application No. 03 100 990.5 filed on Apr. 11, 2003. 
     FIELD OF THE INVENTION 
     This invention relates to a cable drum in general and a construction kit for such a drum in particular. 
     BACKGROUND OF THE INVENTION 
     1. Prior Art 
     Known cable drums comprise a drum body which is supported in bearings free to rotate on an axle and forms a winding surface for a cable between two lateral round plates. One or more spiral springs exert a force opposite to the direction of unwinding, so that while it is being unwound, the cable is kept under initial tension. As derivatives, there are cable drums designed to unwind to the left and cable drums designed to unwind to the right. 
     To simplify stock management, EP 0802601 proposes a spring-driven cable drum, which can be converted so as to unwind in the desired direction. These cable drums consist basically of a drum shell forming the winding surface for the cable, two lateral drum plates, one of them incorporating a bearing, a slip ring unit with a common axle, a lateral fixing flange for the free end of this axle, an enclosed spring cassette pushed on to the axle over a spring anchor hub and a set collar to fix the spring nut on the axle. Should a change of unwinding direction from left to right be desired, the fixing flange is freed and the drum plate and bearing withdrawn from the axle. The spring cassette and the spring anchor hub can then be taken out of the drum shell, as also the set collar. The spring cassette, spring anchor hub and set collar are then turned through 180° and pushed on to the common axle again in reverse order. Finally, the drum plate with the bearing and the fixing flange are fitted again. As this conversion is relatively complicated, it normally has to be carried out by a specialist. 
     A task of this invention was to make available to the end user a construction kit with which he could build, all in one and in the simplest possible way, a cable drum unwinding to the left and a cable drum unwinding to the right. This task is fulfilled by a construction kit according to the present invention. 
     2. Description of the Invention 
     OBJECTS AND SUMMARY OF THE INVENTION 
     A construction kit for a spring-driven cable drum according to the invention consists of a pre-assembled drum core the housing of which forms a winding surface for the cable and containing at least one spiral spring and at least one spring anchor hub, this pre-assembled drum core having an axle channel without an axle passing right through it and the spring anchor hub being fixed to all intents and purposes axially to this axle channel. This construction kit is supplied with a separate axle which can be inserted into the axle channel from either side of the pre-assembled drum core, so designed that the insertion of the axle in either direction creates a form-fit rotary coupling between the spring anchor hub and the axle. Use of this kit provides the means to determine the unwinding direction of the cable drum in the simplest possible way by turning the whole pre-assembled drum core round. It may be noted furthermore that such a construction kit according to the invention can be very easily and safely packed for dispatch. 
     The form-fit rotary coupling between the spring anchor hub and the axle can consist, for example, of a spline or a key. By preference, a cylindrical key will be used, fitting loosely into a longitudinal bore in the spring anchor hub, the axle being provided with a longitudinal cylindrical key groove. 
     The pre-assembled drum core is preferably provided with two ball bearings of equal size, each one constituting an exit hole of the axle channel, thus providing symmetrical support for the cable drum. 
     In its standard version, the construction kit also includes a fixing flange which is or can be fixed to one end of the axle. This fixing flange can then advantageously be provided with a cylindrical extension of such size as to form a close sliding fit with the inner ring of the ball bearing. In the inner ring of the other ball bearing, a bush can then advantageously be fitted, similarly of such size as to form a close sliding fit with this inner ring. 
     For most applications, the construction kit also includes a slip ring unit with a fixed slip ring stack clamped to the other end of the axle and a slip ring unit housing. On each side of the pre-assembled drum core, means of attachment for the slip ring unit housing are then provided, so that the slip ring unit can be fixed to either side of the pre-assembled drum core, depending on the desired direction of unwinding. 
     Two spring units are normally arranged inside the pre-assembled drum core. The first spring unit comprises a first spring cassette and a first spiral spring, the outer end of the first spiral spring being supported by the first spring cassette. The second spring unit comprises a second spring cassette and a second spiral spring, the outer end of the second spiral spring being supported by the second spring cassette. A first spring anchor hub is supported by the inner end of the first spiral spring co-axially with the axle channel. 
     In a first embodiment, a second spring anchor hub is supported by the inner end of the second spiral spring axially in the axle channel. When the axle is inserted in the axle channel, a form-fit rotary coupling is constituted between the first spring anchor hub and the axle and between the second spring anchor hub and the axle. In this first embodiment, both spring cassettes are attached to the drum core, unable to rotate with respect to the latter, so that the first and second spiral springs are coupled in parallel. For the attachment of at least one of the spring cassettes, unable to rotate with respect to the housing of the drum core, the construction kit advantageously includes at least one locking pin. 
     In a second embodiment, a second spring anchor hub is attached to the first spring cassette, unable to rotate with respect to the latter. When the axle is inserted in the tube, a form-fit rotary coupling is constituted between the first spring anchor hub and the axle, but not between the second spring anchor hub and the axle. In this embodiment, the second spring cassette is fixed, unable to rotate, to the drum core, but the second spring cassette is not, so that the first and second spiral springs are coupled in series. 
     The pre-assembled drum core is preferably mounted on a cylindrical body, the outer surface of which forms a direct winding surface for a cable. The construction kit includes a set of round plates, one of which can be attached to each side of the pre-assembled drum core. As round plates of a variety of sizes and designs can be screwed on to the drum core, a single drum core can cover a wide field of applications. This also makes it much easier to protect the round plates, which are not yet fitted to the drum core, against damage during transport. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In what follows, the invention will be described in greater detail with reference to the attached drawings. These show the following: 
         FIG. 1 : a longitudinal section through a spring-driven cable drum, with two spiral springs coupled in parallel; 
         FIG. 2 : a cross section along the line  2 - 2 ′ in  FIG. 1 ; 
         FIG. 3 : a cross section along the line  3 - 3 ′ In  FIG. 1 ; 
         FIG. 4 : a longitudinal section through a spring-driven cable drum, with two spiral springs coupled in series; 
         FIG. 5 : a cross section along the line  5 - 5 ′ in  FIG. 4 ; 
         FIG. 6 : a cross section along the line  6 - 6 ′ in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     The spring-driven cable drum  10  shown in the Figures is assembled from a construction kit according to the invention, for which essentially the following components are required: a pre-assembled drum core  12 , a fixing flange  14 , an axle  16 , a bush  18 , a pair of round plates  20 ,  20 ′ and a slip ring unit  22 . 
     The pre-assembled drum core  12  comprises a cylindrical housing which basically consists of two end plates  26 ,  26 ′ and a shell  28 . The two end plates  26 ,  26 ′ are held together axially by screwed rods (not shown). The shell  28  is clamped between the two end plates  26 ,  26 ′ and forms a winding surface for a cable (not shown). This winding surface is bounded laterally by the two round plates  20 ,  20 ′, which are fastened by means of screws  30  (indicated only by dotted lines) to the end plates  26 ,  26 ′. Each of the end plates  26 ,  26 ′ is mounted on a ball bearing  32 ,  32 ′ with its outer ring pressed into a bore. The two ball bearings  32 ,  32 ′ are identical and in particular have an identical internal bearing diameter. They constitute the openings at the ends of an axle channel in the pre-assembled drum core  12 . 
     The fixing flange  14  comprises a fixing plate  34  and a socket  36  centrally bored to accommodate the axle  16 . The latter has an assembly end  38  which is inserted in the bore in the socket  36  and held there by a clamping screw  39 . The front end of the socket  36  takes the shape of a cylindrical extension  40  of such size that it forms a close sliding fit in the inner ring of the ball bearing  32 . The inner ring  42  is positioned coaxially and in contact with a shoulder surface  44  of the socket  36 . A lip seal  46  seals the annular crevice between the end plate  26  and the socket  36 . 
     The second ball bearing  32 ′ accommodates the bush  18  which is similarly of such size as to form a dose sliding fit in the inner ring  42 ′ of the ball bearing  32 ′. The bush  18  can be slid along the axle  16  and is positioned with a shoulder surface  44 ′ in contact with the inner ring  42  of the ball bearing  3 Z. The other end  50  of the axle  16  projects out of the bush  18 . The bush  18  is held in place longitudinally on the axle  16  by means of a retaining ring  51 . The longitudinally secured bush  18  thus holds the pre-assembled drum core  12  with the inner ring  42  of its ball bearing  32  in contact with the shoulder surface  44  of the fixing flange  14  opposite to it. The retaining ring  51  may be, for example, a retaining ring to DIN  471 . 
     The slip ring unit  22  comprises in its essentials a slip ring stack  52  with slip rings, collector brushes  56  and an enclosed housing  60  in two parts. The slip ring stack  52  is fastened to the second end  50  of the axle  16  by a locking screw  62 . The housing  60  is screwed to the end plate  26 ′ with screws  66 . The collector brushes  56  are fixed to the housing  60 . When the drum core  12  rotates about the axle  16 , the collector brushes  56  consequently rotate about the stationary slip ring stack  52 . 
     Inside the drum core  12  two spring units  70 ,  70 ′ are arranged axially one behind the other between the two end plates  26 ,  26 ′. Each spring unit  70 ,  70 ′ contains a spring cassette  72 ,  72 ′ and a spiral spring  74 ,  74 ′ enclosed in the spring cassette  72 ,  72 ′. As shown in  FIGS. 2 and 3 , the outer end  76 ,  76 ′ of each of the spiral springs  74 ,  74 ′ engages with an anchor strip  78 ,  78 ′ in the spring cassette  72 ,  72 ′. Inside the innermost spiral coil  79 ,  79 ′ of each spiral spring  74 ,  74 ′ a spring anchor hub  80 ,  80 ′ is provided. The inner end of the spiral spring  74 ,  74 ′ seats here on a shoulder surface  81 ,  81 ′ of its spring anchor hub  80 ,  80 ′. It may also be noted that when the axle  16  is removed, the spring anchor hub  80 ,  80 ′ of each spiral spring  74 ,  74 ′ is held to all intents and purposes on the axis of the open axle channel of the pre-assembled drum core  12 . 
     Each of the spring anchor hubs  80 ,  80 ′ has a hole  82 ,  82 ′ for the axle  16  bored through it. By means of a key  84  or  84 ′, as the case may be, a form-fit coupling can be effected between the spring anchor hub  80  or  80 ′, as the case may be, and the axle  16  by the insertion of the axle  16  into the axle channel, so that the inner end of the spiral spring  74 ,  74 ′ can be fixed to the stationary axle  16  by means of the spring anchor hub  80  or  80 ′, as the case may be. The keys  84 ,  84 ′ should preferably by cylindrical keys pushed into key grooves  86 ,  86 ′ in the spring anchor hubs  80 ,  80 ′. These key grooves  86 ,  86 ′ are positioned in the spring anchor hubs  80 ,  80 ′ along the length of the holes  82 ,  82 ′ In such a way that the cylindrical keys  84 ,  84 ′ project partially into the holes  82 ,  82 ′. When the axle  16  is inserted, the cylindrical key  84 ,  84 ′ interacts with a cylindrical key groove  88  made longitudinally in the outer surface of the axle  16 . This creates a form-fit rotary coupling between the spring anchor hub  80  or  80 ′, as the case may be, and the axle  16 . However, if no key is inserted in the key grooves  86 ,  86 ′ of the spring anchor hubs  80 ,  80 ′, these spring anchor hubs  80 ,  80 ′ can be rotated with respect to the axle  16 . 
     In the embodiment shown in  FIGS. 1 to 3 , a key  84 ,  84 ′ has been inserted in the key groove  86 ,  86 ′ of each of the spring anchor hubs  80 ,  80 ′. The spring cassettes  72 ,  72 ′ are also attached, unable to rotate, to the housing. For this purpose, the spring cassette  72 ′ can for example be screwed firmly to the end plate  26 ′ by means of screws  89 , and the spring cassette  72  can be locked unable to rotate by means of pins  90 . By this means, the two spiral springs  74 ,  74 ′ are coupled in parallel, thus doubling their available spring force. 
     In the embodiment shown in  FIGS. 4 to 6 , a key  84 ′ is inserted in the key groove  86 ′ of the spring anchor hub  80 ′. The key groove  86  of the spring anchor hub  80 , however, to which the spring cassette  72 ′ is screwed, is empty. The spring cassette  72  is attached unable to rotate to the drum core  12 , while the spring cassette  72 ′ is not. By this means, the two spiral springs  74 ,  74 ′ are coupled in series, thus doubling their available retraction capacity. 
     It should be noted that it is possible to reverse the direction of unwinding of the spring-driven cable drum  10  without extracting the spring units  70 ,  70 ′, and even without opening the drum core  12 . In fact, the unwinding direction of the spring-driven cable drum  10  can be set simply by fitting the fixing flange  14  either to side A or to side B of the drum core  12 . To reverse the unwinding direction of the spring-driven cable drum  10  in  FIG. 1  or  2 , it is thus only necessary to remove the slip ring unit  22 , then pull the drum core  12  off the axle  16 , extract the bush  18  from the ball bearing  32 ′ and insert it in the ball bearing  32  before putting the drum core  12  back on to the axle  16 , this time with side B towards the fixing flange  14 , and mounting the slip ring unit  22  on side A of the drum core  12 . 
     It should also be noted that a construction kit for a spring driven cable drum according to the invention can be packed for transport relatively easily and safely because the pre-assembled drum core  12 , the axle  16 , the round plates  20 ,  20 ′ and the slip ring unit  22  can be packed in the crate as separate parts. 
     The spring-driven cable drum  10  can be very easily assembled by the customer, who can choose the desired unwinding direction of the spring-driven cable drum  10  during assembly at no additional cost, simply by positioning either side A or side B of the drum core  12  against the fixing flange  14 . 
     The fact that round plates  20 ,  20 ′ in a variety of sizes and versions can be screwed on to the drum core  12  means that a single drum core  12  can be used for a wide field of applications. 
     By coupling the spiral springs  74 ,  74 ′ either in parallel or in series as described above, it is possible in the simplest possible way to double their spring force or retraction capacity respectively.