Abstract:
The invention relates to a device for the inductive transmission of electrical power, comprising a power line which is situated on the primary side of said device and which consists of two wires which are guided in a parallel manner relative to each other. Power can be drawn from line by at least one mobile consumer, which is situated on the secondary side, by means of inductive coupling. Said device is provided with a data line which is situated on the primary side for the additional inductive transmission of data to and/or from the consumer. Said data line consists of two wires which are guided in a parallel manner relative to each other. Each of the data line wires is arranged adjacent to one of the two power line wires and in a manner that is symmetrical to a plane. The cross section of the conductor of the adjacent wire of the energy line is also symmetrical relative to the plane. The inductive coupling between the power line and the data line can be thus kept very low, and simultaneously enables the inductor, which is to be provided on the secondary side for the magnetic coupling with the data line, to be integrated into or mounted on the energy-transmitting consumer. The data line can be fixed to the power line or both lines can be integrated therewith in a common cable.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage entry of co-pending International Patent Application No. PCT/EP02/06765, filed on Jun. 19, 2003 by BÖHLER, Frank et al. entitled DEVICE FOR THE INDUCTIVE TRANSMISSION OF ELECTRICAL POWER, the entire contents of which is imcorporated by reference, and for which priority is claimed under 35 U.S.C. § 371. As in the parent International Application No. PCT/EP02/06765, priority is also claimed to co-pending Germany Patent Application No. 101 31 905.3, filed on Jul. 4, 2001, the entire contents of which is incorporated by reference for which priority is claimed under 35 U.S.C. § 119. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a device for inductive transmission of electric power. 
     A similar device, which is known for example from WO 92/17929, serves for transmission of electrical power to at least one mobile pick-up without a mechanical or electrical contact. It comprises a primary and a secondary part, which are electromagnetically coupled similarly to the transformer principle. The primary part consists of input electronics and a conductor loop deployed along a path. One or more pick-ups and the associated electronic components of the pick-up form a secondary part. In contrast to a transformer, when a primary and a secondary part are coupled together as closely as possible, a loosely coupled system is created. This system can be realized with a relatively high operating frequency in the kiloherz range, which makes it possible to create a bridge even between large air gaps of up to several centimeters. In this case, the operating frequency is determined on the secondary side as a resonance frequency, which is formed with a parallel connection of a condenser to a pick-up coil. 
     Among the advantages of this type of power transmission are in particular freedom from the wear and tear maintenance, as well as the safety of the contact and a degree of availability. Typical applications are in the area of material transport systems for the manufacturing technology, but also for personal transport systems such as elevators and electrically driven buses. Many of these applications require a connection for communication between a central control station and the mobile pick-up, in particular for controlling the pick-up with remote control. Moreover, in a system that has a plurality of pick-ups it can be also desirable for the pick-ups to be able to communicate with each other, for instance in order to coordinate independently their movements and to prevent collisions. Based on the existing state of art, similar communication is normally achieved in the form of radio communication. 
     BRIEF SUMMARY OF THE INVENTION 
     The basic task of the present invention is to indicate a new way for transfer of information to a mobile pick-up and to provide a cable that is suitable for this purpose with a device for inductive transmission of electrical power. 
     This task is solved with a device having the characteristics of the claimed invention. 
     The invention utilizes the fact that the principle of inductive coupling is readily applicable not only to power transmission, but also to data transmission, and that with the laying of a primary conductive loop, the laying of a data line deployed in parallel thereto involves only a very small additional expenditure. This concept, however, results in the problem that the data line must be inductively coupled sufficiently closely to the mobile pick-up with its associated reception and/or transmission direction, while at the same time, it must be decoupled as far as possible from the power line. The invention solves this problem with a special, geometrical arrangement of the data line relative to the power line. 
     It is particularly advantageous to utilize a cable that has been specifically optimized for a combination of a data line with a power line in accordance with this invention, wherein the expenditure required for the joint laying of both lines as well as the risk of a faulty laying is greatly reduced. A further advantage of such a cable, in which both lines have been integrated, is a higher resistance to bending when compared to two separate cables, while fewer attachment points will be required with a hanging arrangement in order to maintain a prescribed maximum length. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is a description of embodiments of the invention based on the figures. The figures indicate the following: 
         FIG. 1  is a schematic, lengthwise view of a device according to the invention, 
         FIG. 2  is a schematic, cross-sectional view of a first embodiment form of the device according to  FIG. 1 , 
         FIG. 3  is a schematic, cross-sectional view of another embodiment form of the device according to  FIG. 1 , and 
         FIG. 4  A-C is a schematic, cross-sectional view of a different embodiment of a special cable according to this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown schematically in  FIG. 1 , a system for inductive transmission of electrical power comprises power supply electronics  1 , and a power line  2 , as well as one or a plurality of mobile pick-ups  3 A through  3 C, while 3 pick-ups represented by pick-ups  3 A through  3 C are employed in  FIG. 1  for purely illustrative purposes. The power supply electronics  1  furnish alternating current to the power line  2 , which is formed as a loop, while each respective pick-ups  3 A through  3 C is inductively coupled thereto. Each pick-up  3 A through  3 C represents at the same time a constituent part of a mobile user along the power line  2  because the pick-up is provided with alternating voltage thanks to said inductive coupling. This voltage can be converted depending on the need of pick-up. It is thus possible for example to produce direct voltage in this location by means of a rectifier and a switch controller of a known art. 
     In accordance with the invention, a data line  4  runs parallel to the power line  2 , which is connected via the supply electronics  1  directly to a combined transmission and reception device  5 , hereinafter referred to as a transceiver. On the side of each pick-up  3 A through  3 C are also provided transceivers  6 A through  6 C, while each of them is inductively coupled with the data line  4 . Information is transmitted between the transceiver  5  and the transceivers  6 A through  6 C serially, for instance in the form of control commands that are sent to each mobile user, as well as status reports that are sent by individual users. It goes without saying that in principle, a pure sender on one side can be also combined with one or several pure receivers on the other side, provided that bidirectional communication is not of interest. On the other band, bidirectional transceivers  6 A through  6 C can communicate not only with the stationary transceiver  5 , but also with each other. Finally, the data line  4  provides a transmission medium for a serial data bus, through which any complex data can be transmitted based on a suitable protocol from the participants who are connected to it to the stationary transceiver  5 , as well as for the mobile transceivers  6 A Through  6 C. 
     While the inductive transmission of information signals per se has been known in information technology for a long time, for instance from the application of transmitters to resistance transformation or to potential separation, the special feature of the present invention is based on the fact that the primary and secondary sides are not stationary relative to each other, but instead mobile along a long route, and that the transmission of information is achieved also through the inductive power transmission over an almost equal distance. 
     With a parallel deployment of both lines  2  and  4 , based on the fact that a significantly larger magnetic current density is required for power transmission in a determined field than what is required for transmission of information, one has to take into account first of all the crosstalk from the power line  2  to the data line  4 , that is to say interference with the transmitted information signal. In order to suppress this interference as much as possible, the geometrical arrangement illustrated by the cross-sectional view shown in  FIG. 2  is provided by the present invention for the individual wires  2 A and  2 B or  4 A and  4 B. 
     Lines  2  and  4  are deployed in the form of a loop. In this manner, the supplied current flows at any time to the line  2  on the primary side for power transmission, for example in the wire  2 A from the supply electronics  1  and back to the other wire  2 B or vice versa. In an analog manner, the current will flow either from the transceiver  5  into the current supplied in the line  4  or from one of the transceivers  6 A through  6 C into the current induced in the line  4  at any time, for example in the wire  4 A in the direction away from the transceiver  5  and in the other wire  4 B to the transceiver  5  or vice versa. Topologically, this means that the respective wires  2 A and  2 B on the one hand and the wires  4 A and  4 B on the other hand pass over each other in the form of a loop, or are connected with each other in a conductive manner by means of a terminal member. Each of both wires  2 A and  2 B of the power line  2 , comprises, as shown in  FIG. 2  on the wire  2 B, a metallic conductor  7 , which is surrounded by insulation  8 . 
     Analogously, each of both wires  4 A and  4 B of the data line  4  comprises, as shown on the wire  4 B in  FIG. 2 , a metallic conductor  9  that is surrounded by insulation  10 . 
     In order to keep the interference with the information transfer due to the energy transfer as small as possible, the mutual inductance between both lines  2  and  4  must be maintained as small as possible. This means that the magnetic current produced by the current in the power line  2  should be interlinked as little as possible with the data line  4 , that is to say the level of the connection between both wires  4 A and  4 B should create as little permeation as possible. For the portion of the total current that originates from the current in the wire  2 B, this is achieved in an ideal manner with the arrangement according to  FIG. 2 , because the field of a rectilinear current in the cross-sectional plane is developed, as is generally known, tangentially, and the lines of the flux of the current in the wire  2 B, creating a radially symmetrical distribution of the current, which can be presumed here without further complications, are in the form of concentric circles about the center axle of the wire  2   b,  so that the resulting magnetic flux component will be zero due to the level of the connection between the wires  4 A and  4 B. This is achieved by the symmetrical arrangement of both wires  4 A  4 B with respect to the wire  2 B. 
     Although the resulting field of the other wire  2 A, whose magnetic flux lines form concentric circles about the center axis of the wire  2 A, creates a non-fading flux component through the connection level of the wires  4 A and  4 B, this component is significantly less important because the wire  2 A is further away than the wire  2 B. It is clear that the smaller this flux component, the further away the location of the wires  4 A and  4 B from the wire  2 A, and the closer the location of the wire  4 A to the wire  4 B. A reduction of said flux component with a further increase of the distance from the wire  2 A, however, creates a conflict because the line  4  will then no longer be deployed together with the line  2  in a joint channel, and also it will no longer be possible to integrate transceiver  6 A together with the pick-up  3 A in one structural unit as indicated in  FIG. 2 . Finally, the same is also applicable to rotation of both wires  4 A and  4 B by 90 degrees in the clockwise direction about the center axis of the wire  2 B, which would be optimal in view of the minimization of the interlinking with the flux generated by the wire  2 A. A separately deployed data line  4  and/or an arrangement of the transceiver  6 A that is completely separate front the pick-up  3 A would lead to significantly higher system costs. This is contrasted with a reduction of said flux component through a further decrease of the mutual distance between the wires  4 A and  4 B, since this would necessarily also decrease the magnetic coupling between the wire  4  and the transceiver  6 A. 
     The symmetrical arrangement of the data line  4  with respect to one of the wires  2 B in the immediate vicinity thereof thus represents a compromise with respect to suppression of the crosstalk between the power line  2  and the data line  4 , while in order to maximize the magnetic coupling between the data line  4  and the transceiver  6 A, it is effective to select from all arrangements those that are equivalent with respect to the symmetry between the data line  4  and the neighboring wire  2 B of the power line  2 , wherein the data line  4  is located as close as possible to the transceiver  6 A. It goes without saying that with the integration of the transceiver  6 A in the pick-up  3 A, as shown in  FIG. 2 , the transceiver  6 A on the secondary side should be arranged as close as possible to the wire  2 B and thus also to the data line  4 . 
     As an alternative to the arrangement illustrated by  FIG. 2 , both conductors of the data line  4  can be also arranged in such a way so that the same type of symmetry in the adjacent wire  2 B will also be displayed with respect to the distant wire  2 A of the power line  2 . In this respect,  FIG. 3  indicates the above mentioned arrangement as an example, wherein both wires  4 A and  4 B of the data line  4  are rotated in contrast to the arrangement according to  FIG. 2  with respect to the center axis of the adjacent wire  2 B of the power line  2  by 90 degrees in the clockwise direction. Also in this case, no additional interlinking of the data line  4  will be created with the magnetic flux produced by the distant wire  2 A, so that theoretically, no inductive crosstalk of any type occurs. 
     It goes without saying that the position of the transceiver  6 A indicated in  FIG. 3 , which is identical to the one shown in  FIG. 2 , is not optimal. Assuming that the direction of the transceiver  6 A that is illustrated by  FIG. 2  is vertical to the level defined by the center axis of both wires  4 A and  4 B of the data line  4  for maximum sensitivity, which will mean an optimal orientation of the transceiver  6 A in  FIG. 2 , then an equally rotated arrangement of the transceiver  6 A to the right adjacent to the wires  4 A and  4 B would be optimal with the arrangement of the data line  4  that is rotated by 90 degrees in  FIG. 3 . However, this location will be generally unavailable given how difficult it would be to realize branching of the power line  2 , so that the transceiver  6 A must be arranged above the power line  2  also in the embodiment according to  FIG. 3 . This results in a lateral position of the transceiver  6 A, as a compromise between the inductive coupling on the one hand, and the space that is available for integration into or addition to the customer  3 A on the other hand. 
     In addition, the transmission and reception coil of the transceiver  6 A can be also built into its own housing inside the same transceiver diagonally to the outer walls and the direction can thus be varied for maximum sensitivity without rotating the busing. This provides an additional amount of freedom for the accommodation of the transceiver  6 A placed above the power line  2  with a lateral arrangement of the data cable according to  FIG. 3 . 
     The invention, however, is in no way limited to the profile forms of the lines  2  and  4  illustrated by the figures. For example, the wires  2 A and  2 B of the power line  2  can also employ a rectangular profile, which would depend on a rectangular form of the conductor  7 . In this case, the profile of the conductor  7  would require two symmetrical planes and both wires  4 A and  4 B of the data line  4  would have to be arranged symmetrically with respect to one of these symmetrical planes in order to eliminate the flux component originating from the current in the wire  2 B. 
     Moreover, the customer  3 A can also have a different form. For example, a T-shaped or E-shaped customer can be created, in which case a vertical T-crosspiece would be projecting between both wires  2 A and  2 B and both outer legs thereof would be laterally encompassed. Analogously to this case, the transceiver  6 A can also have a different profile form than the form illustrated in  FIG.2 . 
     Furthermore, the arrangement according to the invention can also employ at the same time a data line  4  for both wires  2 A and  2 B for power transmission purposes to make available a second data line  4  for the realization of communication with full duplex operations. In this case, a corresponding transceiver  5  or  6 A through  6 C will be required both on the primary side and on the secondary side for both data lines  4 . Communication in full duplex mode, however, would be also made possible with only one data line  4 , as illustrated in  FIGS. 2 and 3 , by separating both transmission directions in the frequency range. 
     As one can see from  FIGS. 2 and 3 , the data line  4  can be constructed separately from the power line  2 . In order to maintain the defined position of the data line toward the transceiver  6 A, it is advantageous when the data line  4  is attached to the wire  2 B of the power line  2 . This could be achieved for example with gluing or with a common cable binder. A substantially advantageous type of attachment from the viewpoint of an easy assembly is an arrangement of holding clamps in equal intervals along the lines  2  and  4 , wherein the clamps are formed in such a way so that the lines  2  and  4  can be locked by a clamp with a short handle. Both lines  2  and  4  can, however, also be integrated in a joint, special cable, which is by far the easiest method for the laying of the cable. 
       FIGS. 4A through 4C  show three possible variants of such a special cable in profile. In the variant according to  FIG. 4A , the circular insulations  110 A and  110 B of both wires  104 A and  104 B, which together form the data line  4 , are connected through bridges  111 A or  111 B in one piece with the circular insulation  108  of the wire  102 B of the power line  2 . The complete insulation consisting of the parts  108 ,  110 A and  11 B, as well as  111 A and  111 B, is formed during a single operation stage by extrusion around the conductors  107 A,  109 A and  109 B. Due to the unsymmetrical outer form, the position of the conductor  109 A and  109 B on the conductor  107  is clearly visible from outside, so that an erroneous orientation during the deployment is largely prevented. 
     In all the variants shown in  FIGS. 4A through 4C , respective conductors  107 ,  207  and  307  of the power line  2  consist of strands, that is to say of several individual wires insulated from each other, which are wound in a spiral form around a central insulator  112  or  212  or  312 , wherein the spiral winding is not visible in the profile shown in  FIGS. 4A through 4C . Although the profile of the conductors  107 ,  207  and  307  is thus not circular, as is schematically illustrated by  FIGS. 2 and 3 , the current distribution can still be considered as being approximately radially symmetrical. The information regarding the magnetic field in the conductor  7  found in  FIGS. 2 and 3  is thus in the same manner also applicable to the conductors  107 ,  207  and  307  of the cable variants illustrated by  FIGS. 4A through 4C . Moreover, it is also advantageous when the use of strands for the power line  2  is dependant on to what extent radial current displacement is displayed with the respective operation parameters (current and frequency). 
     It is also possible to create a configuration in which no strands are used and in which a conductor with a circular profile as shown in  FIGS. 2 and 3  can be employed. 
     In the variant according to  FIG. 4A , the bridges  111 A and  111 B are relatively thin so that both wires  104 A and  104 B can be separated with the application of a small force from the wire  102 B. This is desirable due to the fact that the beginning of the power line  2  must be connected to supply electronics  1 , while onto other hand, the data line must be connected to a transceiver  5  as one can see from  FIG. 1 . In addition, tuning condensers, not shown in the figure, must be connected to the power line  2  along the course of the power line in order to reset the power line  2  for the operating frequency in resonance predetermined by the supply electronics  1 , while the data line  4  does not require any such tuning condensers. It is thus generally advantageous when the data line  4  can be separated from the power line  2  without a large expenditure in order to connect respective other special system components independently of both lines. 
     The cable variant according to  FIG. 4B  differs from to one shown in  FIG. 4A  in that it is provided with a rectangular profile arrangement of joint insulation  213  in one piece of the conductor  207  of the power line  2  and of both conductors  209 A and  209 B of the data line  4 . Both conductors  209 A and  209 B themselves are arranged in two corners delimiting the side  214  of the insulation  213 . Two slits  215 A and  215 B are created along the cable from said side  214 , so that they are extended at right angles to this side adjacent to the conductors  209 A and  209 B, so that the side  214  can be identified as such from outside. Respective notches  216 A and  216 B are extended along the cable in a position corresponding to the slits  215 A and  215 B on both sides of the insulation adjacent to the side  214 . Each of these notches defines together with the respective adjacent slit  215 A or  215 B a predetermined breaking point  211 A or  211 B, which corresponds to the bridge  111 A or  111 B according to  FIG. 4A , enabling a problem-free separation of the data line  4  from the power line  2 . 
     In contrast to both preceding variants, the third cable variant according to  FIG. 4C  does not presuppose extrusion of the entire insulation in one piece by means of a special tool. Instead, the power line  2  and the data line  4  are according to this variant constructed separately and they are later connected with each other. 
     The profile form of the power line  2  corresponds in this case to that of  FIG. 4A  with a conductor  307  and an associated circular insulation  308 . The data line  4  consists of two conductors  309 A and  309 B, each of which is provided with circular insulation  310 A or  310 B. The latter components are connected with a bridge  317  so as to create one piece. The mutual distance between the conductors  309 A and  309 B is largely determined by the bridge  317  and it is constant in particular in the lengthwise direction of the data line  4 . The data line  4  is in its construction comparable to a 300σ antenna line that is common according to prior art. It would be essentially also conceivable to use a fiat cable with more than 2 wires for the data line  4 , from which only two wires would then be used for data transmission. 
     To create a mechanical connection between both lines, the data line  4  is set up against the power line, wherein the bridge  317  should be preferably flexible, so that the data line  4  can be adjusted in its form to the power line  2  as illustrated by  FIG. 4 . Both lines are then covered by a joint jacket  318 , which should be preferably made of a textile or textile-reinforced material. Since in both of these variants, the position of the data line with respect to the power line is not visible as such on the outer form of the cable, this position should be preferably indicated with color coding, for example by a strip  319  deployed in the center of the data line  4 , on the outer side of the jacket  318 . The variant according to  FIG. 4C  is in particular advantageous when the total required length of the cable would not justify the expenditure required for extrusion of the insulation in one piece from an economical viewpoint. 
     To enable a distinction based on the frequency, it is effective when the information signal is in a higher frequency range than the power signal, for example in the range of several Megahertz. A digital modulation procedure of known art can be selected for input of digital information, for example frequency switching (FSK). 10 to 150 kBit/s can be estimated as a rough basis of evaluation for the applicable range of the transmission rate, wherein the carrier frequency must be adjusted in a suitable manner as is generally known. Depending on the application, the length of the transmission route, which corresponds to the length of the range of the movement of the service user, will be variable within a wide range, that is to say from about 1 meter to several hundred meters.