Patent Publication Number: US-7911307-B2

Title: Rotary transformer

Description:
This application is based on and claims priority to German Application No. 103 51 117.2, filed Nov. 3, 2003 and International Application No. PCT/EP2004/012360, filed Nov. 2, 2004 designating the U.S., the entire contents of both of which are hereby incorporated by reference. 
     The invention relates to a rotary transformer as claimed in the precharacterizing clause of claim  1 . The invention can be used, for example, in welding robots. 
     EP 0 722 811 B1 has disclosed a wireless robot having an apparatus for transmitting electrical power which comprises a rigid core bearing an articulated joint and having a primary winding around a proximal part of a rotary shaft and a rotary core having a secondary winding about a distal part of the rotary shaft, the rigid core being positioned opposite the rotary core in contactless fashion, in order to transmit electrical power from the proximal part to the distal part in contactless fashion by means of electromagnetic radiofrequency induction. 
     EP 0 598 924 B1 has disclosed a contactless power transmission apparatus for a machine device, in which case power is transmitted from a stationary unit to a rotary unit of the machine device without any direct electrical contact. A split core is used which comprises a first core and a second core, these cores being fixed to the stationary unit and the rotary unit, respectively, and forming a magnetic circuit, whose magnetic path length does not change as a result of any desired rotation of the second core in relation to the first core. A first coil is connected to a radiofrequency AC source and is provided in the stationary unit in order to provide the magnetic circuit with a magnetomotive force. A second coil is connected to a power-receiving apparatus and is fixed to the rotary unit, the second coil being arranged such that it is connected to a magnetic flux which passes through the magnetic circuit. 
     EP 0 680 060 A1 has disclosed a rotary transformer having an annular stator, which is U-shaped in cross section, and a rotor. The sleeve-shaped primary coil is wound around the inner limb of the stator, while the likewise sleeve-shaped secondary coil conforms to the outer limb of the rotor, with the result that, whilst forming an air gap ensuring that they can move in relation to one another, the primary coil and the secondary coil lie directly opposite one another. 
     Rotary transformers in accordance with the prior art have distributed windings, i.e. the primary winding and the secondary winding are located in core halves which are separate from one another and in each case do not protrude beyond said core halves. On the one hand, a considerable leakage field is formed, and on the other hand the losses of the rotary transformer are relatively high. 
     The invention is based on the object of specifying a rotary transformer which has a relatively high degree of efficiency even when subjected to a radiofrequency—for example 25 kHz—and produces a relatively low leakage field. 
     This object is achieved according to the invention, in conjunction with the features of the precharacterizing clause, by the features specified in the characterizing clause of claim  1 . 
     The advantages which can be achieved by the invention consist in particular in the fact that the skin effects occurring at high frequencies as well as the transformer losses occurring and the leakage field occurring are minimized. This therefore results in a high degree of efficiency for the rotary transformer. The rotary transformer can be reproduced exactly, i.e. the discrepancies in the electrical data occurring during manufacture are extremely slight. The air gap to be formed between the two core halves—important for the two transformer halves to be capable of moving in a rotary fashion freely with respect to one another—can be selected such that it has a relatively large dimension and has a negligible effect on the leakage field produced and the losses produced. 
     The primary part and the secondary part of the rotary transformer can be used at the same time as DC-isolated “contacts” in the sense of a plug; for example the primary part is located at the free end of one robot arm, which can be fitted with various tool arms. These different tool arms each have the secondary part of the rotary transformer at their end which serves to fix it to the robot arm. It is possible for tools to be replaced in a simple and rapid manner, i.e. for various tool arms to be fitted to the robot arm. 
     Further advantageous are described in the description below. 
     Advantageous refinements of the invention are characterized in the dependent claims. 
    
    
     
       The invention will be explained below with reference to the exemplary embodiments illustrated in the drawing, in which: 
         FIG. 1  shows a section through a first exemplary embodiment of a rotary transformer having winding sections extending parallel to the axis of rotation, 
         FIG. 2  shows a section through a second exemplary embodiment of a rotary transformer having winding sections extending perpendicularly with respect to the axis of rotation, 
         FIG. 3  shows a section through a third exemplary embodiment of a rotary transformer having a plurality of annular cutouts in the core halves, 
         FIGS. 4 ,  5  show perspective illustrations of exemplary embodiments with a central hole in the core, and 
         FIG. 6  shows the course of the magnetic field strength over the individual winding sections. 
     
    
    
       FIG. 1  shows a first exemplary embodiment of a rotary transformer having winding sections extending parallel to the axis of rotation. In this embodiment, the primary winding and the secondary winding have in each case sleeve-shaped winding sections which interengage in the manner of a comb. This embodiment is advantageous in the case of rotary transformers in which the physical height is intended to be great in comparison to the diameter of the core. 
     The rotary transformer  1  has two essentially symmetrical core halves, to be precise a first core half having a base plate  2 , an outer ring  3  and an inner cylinder  4  as well as a second core half having a base plate  5 , an outer ring  6  and an inner cylinder  7 . An air gap  8  is formed between the two core halves, with the result that the two core halves can move in rotary fashion with respect to one another about a common axis of rotation  9 , which runs in the center of the inner cylinders  4 ,  7 , without coming into contact. 
     As can clearly be seen in the sectional illustration shown in  FIG. 1 , the outer rings  3 ,  6 , the inner cylinders  4 ,  7  and the base plates  2 ,  5  delimit a single annular cutout which is suitable for accommodating (in each case preferably helical) windings. The individual winding sections of the primary winding and the secondary winding are in this case fixed in circular winding supports, which are in each case made from an electrically insulating material, for example plastic, and are mounted on the inner sides of the base plates. The electrical connections between the individual, in each case sleeve-shaped winding sections run within the winding supports. Each winding has two winding terminations, which are passed to the outside via the winding support and corresponding openings in the base plate. 
     A winding support  10 , which is associated with the primary winding, is fixed to the base plate  2  of the first core half and fixes, for example, five winding sections of a primary winding, to be precise
         an outer winding section  11 ,   two immediately adjacent central winding sections  12 ,  13 ,   two immediately adjacent inner winding sections  14 ,  15 .       

     A winding support  17 , which is associated with the secondary winding, is fixed to the base plate  5  of the second core half and fixes five winding sections of a secondary winding, to be precise
         two immediately adjacent outer winding sections  18 ,  19 ,   two immediately adjacent central winding sections  20 ,  21 ,   an inner winding section  22 .       

     A winding termination  16  of the primary winding and a winding termination  23  of the secondary winding can be seen (of course at least two winding terminations are required per winding). 
     As is identified in  FIG. 1 , the current directions of the winding sections (which lie directly opposite one another so as to form an air gap and are associated alternately with the primary winding and the secondary winding)  11 / 18 ,  19 / 12 ,  13 / 20 ,  21 / 14 ,  15 / 22  are in each case opposite one another. 
       FIG. 2  illustrates a second exemplary embodiment of a rotary transformer having winding sections extending perpendicularly with respect to the axis of rotation. In this embodiment, the primary winding and the secondary winding have in each case circular winding sections which interengage in the manner of a comb. This embodiment is advantageous in the case of rotary transformers in which the diameter is intended to be large in comparison to the physical height. 
     The rotary transformer  24  has two asymmetrical core halves, to be precise a first core half having a base plate  25  and an inner cylinder  26  as well as a second core half having a base plate  27  and an outer ring  28 . An air gap  29  is formed between the base plate  27  and the inner cylinder  26 , and an air gap  30  is formed between the base plate  25  and the outer ring  28 , with the result that the two core halves can move in rotary fashion with respect to one another about a common axis of rotation  31 , which runs in the center of the inner cylinder  26 , without coming into contact. 
     As can clearly be seen in the sectional illustration shown in  FIG. 2 , the outer ring  28 , the inner cylinder  26  and the base plates  25 ,  27  delimit a single annular cutout which is suitable for accommodating (in each case preferably helical) windings. The individual winding sections of the primary winding and the secondary winding are in this case fixed in sleeve-shaped winding supports, which are in each case made from an electrically insulating material, for example plastic, and are mounted on the inner side of the outer ring  28  or the outer side of the inner cylinder  26 . The electrical connections between the individual, in each case circular winding sections run within the winding supports. Each winding has two winding terminations, which are passed to the outside via the winding support and corresponding openings in the base plate. 
     A winding support  32 , which is associated with the primary winding, is fixed to the outer side of the inner cylinder  26  of the first core half and fixes, for example, five winding sections of a primary winding, to be precise
         a winding section  33 ,   two immediately adjacent winding sections  34 ,  35 ,   two immediately adjacent winding sections  36 ,  37 .       

     A winding support  39 , which is associated with the secondary winding, is fixed to the inner side of the outer ring  28  of the second core half and fixes five winding sections of a secondary winding, to be precise
         two immediately adjacent winding sections  40 ,  41 ,   two immediately adjacent central winding sections  42 ,  43 ,   a winding section  44 .       

     A winding termination  38  of the primary winding and a winding termination  45  of the secondary winding can be seen. 
     As is identified in  FIG. 2 , the current directions of the winding sections (which lie directly opposite one another so as to form an air gap and are associated alternately with the primary winding and the secondary winding)  33 / 40 ,  41 / 34 ,  25 / 42 ,  43 / 36 ,  37 / 44  are in each case opposite one another. 
       FIG. 3  illustrates a third exemplary embodiment of a rotary transformer having a plurality of annular cutouts in the core halves. This embodiment is in principle suitable both for sleeve-shaped winding sections—see FIG.  1 —and for circular winding sections—see  FIG. 2 , but only one embodiment, corresponding to  FIG. 1 , is shown, with sleeve-shaped winding sections. 
     The rotary transformer  46  has two essentially symmetrical core halves, to be precise a first core half having a base plate  47 , an outer ring  48 , two intermediate rings  49 ,  50  and an inner cylinder  51  as well as a second core half having a base plate  52 , an outer ring  53 , two intermediate rings  54 ,  55  and an inner cylinder  56 . An air gap  57  is formed between the two core halves, with the result that the two core halves can move in rotary fashion with respect to one another about a common axis of rotation  58 , which runs in the center of the inner cylinders  51 ,  56 , without coming into contact. 
     As can clearly be seen in the sectional illustration in  FIG. 3 , the outer rings  48 ,  53 , the intermediate rings  49 / 54 ,  50 / 55 , the inner cylinders  51 / 56  as well as the base plates  47 / 52  delimit three separate and concentrically arranged annular cutouts which are suitable for accommodating (in each case preferably helical) windings. The individual winding sections of the primary winding and the secondary winding are in this case fixed in circular winding supports, which are in each case made from an electrically insulating material, for example plastic, and are mounted on the inner sides of the base plates. The electrical connections between the individual, in each case sleeve-shaped winding sections run within the winding supports. Each winding has two winding terminations, which are passed to the outside via the winding support and corresponding openings in the base plate. 
     An outer winding support  59 , which is associated with the primary winding, is fixed to the base plate  47  of the first core half at the location of the outer annular cutout and fixes two winding sections of a primary winding, to be precise
         an outer winding section  62 ,   an inner winding section  63 .       

     A central winding support  60 , which is associated with the primary winding, is fixed to the base plate  47  of the first core half at the location of the central annular cutout and fixes two winding sections of a primary winding, to be precise
         an outer winding section  64 ,   an inner winding section  65 .       

     An inner winding support  61 , which is associated with the primary winding, is fixed to the base plate  47  of the first core half at the location of the inner annular cutout and fixes two winding sections of a primary winding, to be precise
         an outer winding section  66 ,   an inner winding section  67 .       

     An outer winding support  68 , which is associated with the secondary winding, is fixed to the base plate  52  of the second core half at the location of the outer annular cutout and fixes two immediately adjacent winding sections  71 ,  72  of a secondary winding. 
     A central winding support  69 , which is associated with the secondary winding, is fixed to the base plate  52  of the second core half at the location of the central annular cutout and fixes two immediately adjacent winding sections  73 ,  74  of a secondary winding. 
     An inner winding support  70 , which is associated with the secondary winding, is fixed to the base plate  52  of the second core half at the location of the inner annular cutout and fixes two immediately adjacent winding sections  75 ,  76  of a secondary winding. 
     As is identified in  FIG. 3 , the current directions of the winding sections (which lie directly opposite one another so as to form an air gap and are associated alternately with the primary winding and the secondary winding)  62 / 71 ,  72 / 63 ,  64 / 73 ,  74 / 65 ,  66 / 75 ,  76 / 67  are in each case opposite one another. 
     Additional advantages of this embodiment as shown in  FIG. 3 :
         It is also possible for a plurality of DC-isolated primary windings and secondary windings to be provided, i.e. it is possible for a plurality of circuits to be inductively coupled into one and the same rotary transformer.   As regards the magnetic flux there is a shortened path length, which reduces the losses and thus increases the degree of efficiency.   Overall less core material is required for guiding the magnetic flux.   In comparison to the exemplary embodiments shown in  FIG. 1  and  FIG. 2 , a greater primary/secondary transformation ratio can be selected.       

       FIGS. 4 and 5  illustrate exemplary embodiments with a central hole in the core, to be precise  FIG. 4  essentially corresponds to the embodiment shown in  FIG. 1  and  FIG. 5  essentially corresponds to the embodiment shown in  FIG. 2 . 
       FIG. 4  shows a rotary transformer  77  which has a first core half  78  and a second core half  79 , which is formed essentially symmetrically with respect thereto, an air gap  80  being formed between the two core halves, and a central hole  81  being provided in the core halves. A winding system  82 , comprising a primary winding and a secondary winding, is located in the annular cutout in the rotary transformer  77 , the inner cylinders  4 ,  7  of the embodiment shown in  FIG. 1  being replaced by inner rings in order to implement the desired central hole  81 . 
       FIG. 5  shows a rotary transformer  83  which has a first core half  84  and a second core half  85 , air gaps  86 ,  87  being formed between the two core halves, and a central hole  88  being provided in the core halves. A winding system  89 , comprising a primary winding and a secondary winding, is located in the annular cutout in the rotary transformer  83 , the inner cylinder  26  of the embodiment shown in  FIG. 2  being replaced by an inner ring in order to implement the desired central hole  88 . 
     Where winding sections have been mentioned above, a winding section may alternatively comprise:
         a single turn or   a plurality of (two, three, four . . . ) turns.       

     The transformation ratio between the primary winding and the secondary winding is in principle freely selectable. 
       FIG. 6  shows the profile of the magnetic field strength over the individual winding sections. If one first considers the exemplary embodiment shown in  FIG. 1 , the magnetic field strength over the winding section  11  increases from 0 to the maximum value MAX, falls to 0 and the minimum value MIN over the winding sections  18  and  19 , respectively, increases to 0 and MAX over the winding sections  12  and  13 , respectively, falls to 0 and MIN over the winding sections  20  and  21 , respectively, increases to 0 and MAX over the winding sections  14  and  15 , respectively, and falls to 0 over the winding section  22 . An identical profile of the magnetic field strength results over the winding sections  33 - 40 - 41 - 34 - 35 - 42 - 43 - 36 - 37 - 44  in the exemplary embodiment shown in  FIG. 2 . 
     Of course, an identical profile for the magnetic field strength is also produced in the exemplary embodiment shown in  FIG. 3 : 0-MAX-0-MIN-0-MAX-0-MIN-0-MAX-0-MIN-0 over the individual winding sections  62 - 71 - 72 - 63 - 64 - 73 - 74 - 65 - 66 - 75 - 76 - 67 . 
     It can easily be seen that this zigzag profile for the magnetic field strength (which occurs in all exemplary embodiments) between a maximum value MAX and a minimum value MIN results from the fact that the winding sections of the primary winding and the secondary winding interengage in the manner of a comb, the current flow of immediately adjacent winding sections of the primary winding and the secondary winding in each case being in the opposite direction. If one were to arrange all of the winding sections of the primary winding next to one another and all of the winding sections of the secondary winding likewise next to one another and the primary winding and secondary winding thus formed opposite one another, as is envisaged in EP 0 680 060 A1, the maximum value of the magnetic field strength of a winding distributed in this manner would be a multiple higher than the maximum value which would be achieved in the arrangement according to the invention with winding sections interengaging in the manner of a comb. As a consequence, on the one hand the transformer losses occurring and on the other hand the leakage field occurring would be a multiple greater. This would thus result in a relatively low degree of efficiency for the rotary transformer. 
     In the above embodiments, it has been assumed by way of example that the primary winding and the secondary winding of the rotary transformer are designed for the same power rating. As a deviation from this, embodiments can of course be realized in which the secondary winding of the rotary transformer is designed to have a lower power capacity than the primary winding and is also correspondingly designed to be lighter if only relatively low powers are to be produced on the secondary side. In such an embodiment, the core half of the secondary part can be dispensed with entirely. This embodiment is very advantageous in particular when using the rotary transformer in a robot having a tool replacement device. A tool replacement device allows for various tool arms to be fitted to the robot arm. The various tools have different power consumptions. The secondary sides of the rotary transformer are in each case matched to the specific power requirement of the tool, while the primary side of the rotary transformer remains the same for all different tools (with different power requirements). 
     In the above embodiments, it has been assumed that the core halves are each of integral design. As a deviation from this, it is also possible, of course, for the core halves or the core to comprise individual segments (for example in the form of “cake slices”). 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Rotary transformer 
           2  Base plate of the first core half 
           3  Outer ring 
           4  Inner cylinder 
           5  Base plate of the second core half 
           6  Outer ring 
           7  Inner cylinder 
           8  Air gap 
           9  Axis of rotation 
           10  Winding support of the first core half 
           11  First winding section of the primary winding 
           12  Second winding section 
           13  Third winding section 
           14  Fourth winding section 
           15  Fifth winding section 
           16  Winding termination 
           17  Winding support of the second core half 
           18  First winding section of the secondary winding 
           19  Second winding section 
           20  Third winding section 
           21  Fourth winding section 
           22  Fifth winding section 
           23  Winding termination 
           24  Rotary transformer 
           25  Base plate of the first core half 
           26  Inner cylinder 
           27  Base plate of the second core half 
           28  Outer ring 
           29  Air gap 
           30  Air gap 
           31  Axis of rotation 
           32  Winding support of the first core half 
           33  First winding section of the primary winding 
           34  Second winding section 
           35  Third winding section 
           36  Fourth winding section 
           37  Fifth winding section 
           38  Winding termination 
           39  Winding support of the second core half 
           40  First winding section of the secondary winding 
           41  Second winding section 
           42  Third winding section 
           43  Fourth winding section 
           44  Fifth winding section 
           45  Winding termination 
           46  Rotary transformer 
           47  Base plate of the first core half 
           48  Outer ring 
           49  Intermediate ring 
           50  Intermediate ring 
           51  Inner cylinder 
           52  Base plate of the second core half 
           53  Outer ring 
           54  Intermediate ring 
           55  Intermediate ring 
           56  Inner cylinder 
           57  Air gap 
           58  Axis of rotation 
           59  Winding support of the first core half 
           60  Winding support 
           61  Winding support 
           62  First winding section of the primary winding 
           63  Second winding section 
           64  Third winding section 
           65  Fourth winding section 
           66  Fifth winding section 
           67  Sixth winding section 
           68  Winding support of the second core half 
           69  Winding support 
           70  Winding support 
           71  First winding section of the secondary winding 
           72  Second winding section 
           73  Third winding section 
           74  Fourth winding section 
           75  Fifth winding section 
           76  Sixth winding section 
           77  Rotary transformer 
           78  First core half 
           79  Second core half 
           80  Air gap 
           81  Central hole 
           82  Winding system 
           83  Rotary transformer 
           84  First core half 
           85  Second core half 
           86  Air gap 
           87  Air gap 
           88  Central hole 
           89  Winding system