Abstract:
A machine tool or a production machine, such as e.g. a multispindle machine, or a robot, is described, wherein a liquid metal lubricated slide bearing is not only used to transmit feed currents for electrical consumers but also to transmit currents for producing control signals. Accordingly, it is possible to apply via the liquid metal lubricated slide bearings a voltage of 600 volts in order to produce feed currents and a voltage of 24 volts in order to produce control signals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2007/053608 filed Apr. 13, 2007 and claims the benefit thereof. The International Application claims the benefits of German application No. 10 2006 028 647.2 DE filed Jun. 22, 2006, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention relates to a machine tool or production machine or robot, with a fixed part and a part that rotates in relation thereto. The machine tool can be a multispindle machine or a revolving transfer machine. Production machines corresponding to the definition are found for example in beverage filling plants. 
     In the case of multispindle machines, a number of spindle motors (electrical consumers) are mounted on the rotating part, known as the drum. 
     In the case of machine tools or production machines or robots of the type mentioned above, it is always problematic supplying consumers on or at the rotating part with currents for feed purposes. At the same time signals to control the consumers have to be transmitted in the case of machine tools or production machines. 
     Generally current is supplied to the rotating part in the field by way of slip rings. These slip rings are subject to mechanical abrasion, in other words wear. Ensuring interruption-free transmission is technically complex. 
     BACKGROUND OF INVENTION 
     It is known from WO 2005/062432 A1 that liquid metal alloys can be used instead of the conventional copper slip ring contacts. To this end a current transmission surface is provided respectively on the fixed part and on the part rotating in relation thereto, with the two current transmission surfaces forming a gap between one another, into which the liquid metal alloy is inserted. This creates an electrical contact and at the same time does not restrict the rotatability of the rotating part in relation to the fixed part. 
     WO 2005/062432 A1 only discloses the transmission of a feed current via three current transmission contact units isolated galvanically from one another. 
     SUMMARY OF INVENTION 
     An object of the invention is to develop a machine tool or production machine of the type mentioned in the introduction in such a manner that both transmission of the feed current and production of control signals are facilitated. 
     This object is achieved by a machine tool or production machine or a robot as claimed in the claims. 
     The fixed part therefore has four current transmission surfaces, which are insulated electrically from one another, and the rotating part also has four such electrically insulated current transmission surfaces, with each of the four current transmission surfaces of the fixed part being assigned respectively to a current transmission surface of the rotating part, a gap being formed between them and a liquid metal alloy being inserted into the gap. This produces a current transmission contact in each instance, overall at least four current transmission contacts. 
     It is then possible for two first current transmission contacts to be deployed to feed a first electrical consumer on the rotating part and two further current transmission contacts to be deployed to feed a second electrical consumer, which produces control signals for the first electrical consumer. 
     The voltage ranges deployed are preferably completely different here. Thus a voltage of 400 to 1000 volts can be applied to the first current transmission contacts and a voltage of 10 to 45 volts can be applied to the further current transmission contacts. Consideration is given here to a voltage of 600 volts, which is required to feed the electrical consumers in the case of a typical multispindle machine, and a voltage of 24 volts, which serves to produce the control signals. 
     A fifth contact, which does not necessarily have to be referred to as a current transmission contact, is preferably connected to ground. In other words there is a fifth contact surface on both the fixed and rotating parts of the machine respectively, together forming a gap, in which the liquid metal alloy is contained, with the entire contact being connected to ground by connecting the fifth contact surface of the fixed part to ground. The voltages applied to the current transmission surfaces are stabilized by the ground connection. 
     In the case of multispindle machines there is commonly an arrangement, in which the fixed and rotating parts respectively are hollow cylinders, with one part enclosing the other and with the part enclosed by the other part having a cylinder wall. When conventional copper slip contacts are used, the power cables are generally guided in the air-filled internal space of the hollow cylinder. It is a particular aspect, irrespective of the use of the four current transmission contacts, that the current supply systems are guided to the current transmission surfaces in the cylinder wall of the part enclosed by the other part. Guiding the current supply systems in the cylinder wall means that the hollow space of the cylinder can be used for other purposes, for example for the passage of other materials, such as cooling and hydraulic oils. 
     The enclosing part can also have a cylinder wall, in which current supply systems are guided to the current transmission surfaces. If the enclosed part is fixed for example, this means that the current supply systems are guided in the cylinder walls in the rotating part too. This produces a relatively compact structure. 
     A further aspect of the invention is the embodiment of the current transmission contacts. This aspect is independent of the invention claimed in the independent claims, even if it is preferably executed at the same time as it. According to this aspect, one of the two parts encloses the other, the fixed part and rotating part being cylindrical. A ring of U-shaped cross-section is provided on one cylinder wall of the one part to provide a current transmission surface. A ring of L-shaped cross-section is provided on the cylinder wall of the other part to provide a current transmission surface. The current transmission contacts are then formed by inserting (a liquid metal alloy) in the ring of U-shaped cross-section and by an arm of the “L” engaging in the “U” and thereby engaging in the liquid metal alloy. The engaging arm of the “L” then has to be sealed off from the two arms of the “U”, so that the liquid metal alloy cannot escape from the U-shaped ring. 
     Using the bending L-shaped ring allows the U-shaped ring to be guided almost up to the other part, to which it is not secured. This allows a particularly compact embodiment of the current transmission contacts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described below with reference to the drawings, in which: 
         FIG. 1  shows a schematic diagram of current transmission, 
         FIG. 2  shows a perspective view of a transmitter unit of an machine with power rails and 
         FIG. 3A  and  FIG. 3B  show perspective views from different directions of an individual element of the transmitter unit from  FIG. 2  with associated power rails. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows the basic structural elements of a machine tool or production machine, namely a fixed part  10  and a rotating part  12 , it being possible to differentiate the parts  10  and  12  due to different shading (see key). 
     The fixed part has a basic body in the form of a hollow cylinder with a cylinder wall  14 . The rotating part also has a basic body in the form of a hollow cylinder with a cylinder wall  16 . The cylinder wall  14  of the fixed part  10  has an insulating ring  18  to separate the cylinder wall  14  into two parts that are insulated from one another. Similarly the cylinder wall  16  of the rotating part  12  has an insulating ring  20 . 
     The rotating part  12  is actually supported in relation to the fixed part  10  by means of radial ball bearings  22  and/or  22 ′. Current transmission contacts  24  and  24 ′ are used for current transmission. The current transmission contacts  24  and/or  24 ′ are formed by two rings  26  and/or  26 ′ and  28  and/or  28 ′. The ring  26  is connected permanently to the cylinder wall  16  of the rotating part  12  and has a U-shaped profile, with one arm  32  of the “U” resting on the inside of the cylinder wall  16 , so that the “U” profile is a horizontal profile. The ring  28  is connected permanently to the cylinder wall  14  of the fixed part  10  and is of L-shaped cross-section. One arm of the “L” here engages between two arms  32  and  32 ′ of the “U”. Between the end of the arm  30  and the ring  26  a gap  34  is formed, into which a liquid metal alloy  34  is inserted. Sealing lips  36  and/or  36 ′ are located between the arm  30  of the L-ring and the arms  32  and/or  32 ′ of the U-ring, so that the liquid metal alloy cannot escape from the U-shaped ring  26 . 
     The arrangement allows rotation of the rotating part  12  in relation to the fixed part  10  about the axis  38 . The bearings  22  and  22 ′ are mainly acting here but the current transmission contacts  24  and/or  24 ′ also function as bearings. They do not prevent rotation, as the liquid metal alloy inside the gap  34  ensures a sliding movement of the ring  26  in relation to the ring  28 , with in particular the arms  32  and  32 ′ of the U-profile rotating about the arm  30  of the L-profile. It is now possible to transmit current with the aid of the current transmission contacts  24  and  24 ′. A corresponding voltage (characterized by the signs “+” and “−”) can be applied by way of power lines  40  and/or  40 ′ to the rings  28  and/or  28 ′. The liquid metal alloy in the gap  34  means that the corresponding voltage is also applied on the side of the rotating part  12  and can be tapped by way of power lines  42  and/or  42 ′. The applied voltage can be a voltage of 600 volts. Such a voltage can be used to feed electrical consumers, which are affixed to the rotating part  12 , with the power lines  42  and  42 ′ having to be connected respectively to the electrical consumers. The power lines  40  and  40 ′ are connected to a fixed device outside the machine, e.g. a control cabinet. 
     As well as the feeding of electrical consumers, activation of the electrical consumers can also take place. In the case of multispindle machines in particular the motors as electrical consumers have a motor controller, to which control signals are to be supplied on the part of the fixed part. The two current transmission contacts  24  and  24 ′ can also be used to transmit such control signals, with the voltage present then being typically 24 volts. 
       FIG. 2  shows a perspective view of a transmitter unit corresponding to  FIG. 1 . It shows the rotating part  12 ′, which is configured as a hollow cylinder, and the fixed part  10 ′.  FIG. 2  shows an addition to the arrangement in  FIG. 1 . The cylinder wall  16 ′ of the rotating part is divided into five electrically insulated elements  46  by four insulating rings  20 ′. The cylinder wall  14 ′ of the fixed part  10 ′ is also correspondingly divided into five electrically insulated elements by four insulating rings  18 ′. A contact in the manner of the current transmission contacts  24  and/or  24 ′ is now to be assigned to each of these five elements  48 ; in other words instead of two contacts  24  and  24 ′ the arrangement according to  FIG. 2  has five such contacts in its interior, which cannot be seen. By providing five current transmission contacts in the manner of the contacts  24  and  24 ′ shown in  FIG. 1  it is possible to apply two voltages, each voltage requiring two of the units, between which the voltage is applied. The fifth unit serves to provide a ground connection. 
     Although in the schematic drawing according to  FIG. 1  the lines  40  and  40 ′ are shown in the hollow space of the cylinder of the fixed part  10 , in reality provision is made for the lines to be configured in the cylinder wall  14 . This is shown clearly in  FIG. 2 , which shows five lines  40 ″, one supply line for each of the elements  46  of the cylinder wall  16 ′ isolated by the insulating rings  20 ′. The individual elements  46 , which are isolated from one another by the insulating rings  20 ′, can be separate components, as shown in  FIG. 3A  and  FIG. 3B . A structural element designated as a whole as  44 , consisting of one structural element  46  for the cylinder wall  16 ′ and one structural element  48  for the cylinder wall  14 ′ is shown. The one current transmission contact in the structural element  44  is not shown. This is a current transmission contact in the manner of the current transmission contact  24  and/or  24 ′ in  FIG. 1 . This contact requires precisely one supply line  40 ″ and one line  42 ″ on the part of the rotating part  12 ′. Five through holes  50  for the lines  42 ″, also from the other four structural elements  46 , are correspondingly provided in the cylinder wall of the component. Five through holes  52  are correspondingly provided in the cylinder wall  48 , also for guiding through the lines  40 ′ from other components  48 . 
     Integrating the power lines  40 ″ and  42 ″ in the respective cylinder walls  14 ′ and/or  16 ′ ensures that the hollow space of the cylinder of the fixed part  10 ″ remains completely empty. Also there are no power lines arranged outside the cylinder wall  16 ′. 
     Material, which is supplied by way of the hollow space of the cylinder of the fixed part  10 ″, can be processed by the machine tool or production machine (e.g. multispindle machine), which uses the transmitter unit according to  FIG. 2 . 
     The present invention is not specifically for a fixed part inside the interior and a rotating part arranged outside. Instead the invention can be realized in a totally analogous manner in the reverse instance, where the rotating part is arranged in the interior of the fixed part.