Patent Publication Number: US-2021184545-A1

Title: System and Method for Ethernet Communication with a Rotary Coupler

Description:
BACKGROUND INFORMATION 
     The subject matter disclosed herein relates generally to providing communication between a rotating object and a stationary object and, more specifically, to a system which utilizes a rotary coupler to provide communication between a rotating member and a stationary member in a rotary machine. 
     A traditional rotary machine includes a stationary member, such as a stator, and a rotating member, such as a rotor. When a machine is being controlled in a motoring operating mode, a controlled voltage is applied to a coil on the stator, where the controlled voltage has a variable magnitude and a variable frequency. The controlled voltage interacts with a magnetic field (e.g., permanent magnet machine) or electromagnetic field (e.g., induction or synchronous machine) emitted from the rotor or with a magnetic saliency (e.g., synchronous reluctance) machine to achieve desired operation of the motor. The rotor may be controlled from zero speed up to hundreds or thousands of revolutions per minute according to the requirements of an application. 
     Historically, there have been no electronic devices mounted on the rotor due, in part, to the challenges of providing power to the rotating member as well as transmitting data back from the rotating member to the stationary member. In recent advances, the present inventors have developed methods for providing power to the rotating member without contact between the rotating member and a stationary member. The recent developments allow for electronic devices to be mounted to and operate on the rotating member, such as the rotor in a motor. However, to fully realize the potential of the contactless power transfer, it is necessary also to provide communication between the rotating member and the stationary member. 
     Traditional wireless communication techniques, such as Bluetooth, ZigBee, or Ultra-wideband (UWB), that are normally well suited for low energy, short range communication face challenges when attempting to implement them within a motor. The data protocols themselves can suffer from a low data transfer rate or from reliability issues. Additionally, the controlled voltage applied to the stator coil is commonly generated using a modulation technique, such as pulse width modulation, which has the potential to generate radiated emissions within the motor that interfere with the wireless data transfer within the motor. Further, a network in communication with the rotating machine typically uses an industrial protocol, such as EtherNet/IP, which would require conversion from the first, wireless protocol into a second communication protocol when the wireless transfer is successful. Thus, these wireless communication techniques are not well-suited for use between a rotor and a stator in a motor. 
     Thus, it would be desirable to provide a contactless Ethernet communication technique adapted for communication between a rotor and a stator in a rotating machine. 
     BRIEF DESCRIPTION 
     According to one embodiment of the invention, a system for providing contactless communication between a rotating member and a stationary member in a rotary machine includes an electronic circuit mounted on the rotating member of the rotary machine, a power supply operative to provide power to the electronic circuit, and a transmitter operatively mounted in the electronic circuit. The transmitter receives power from the power supply and is configured to generate Ethernet data packets. The system also includes a primary winding mounted to the rotating member of the rotary machine and a secondary winding mounted to the stationary member of the rotary machine. The primary winding is electrically connected to the transmitter to receive the Ethernet data packets, and the secondary winding is spaced apart from the primary winding by an air gap. The secondary winding receives the Ethernet data packets via coupling between the primary and secondary windings. A receiver is operatively connected to the secondary winding to receive the Ethernet data packets generated by the transmitter mounted on the rotating member of the rotary machine. 
     According to another embodiment of the invention, a method for providing communication between a rotating member and a stationary member in a rotary machine is disclosed. Ethernet data packets are generated with a transmitter operatively mounted on the rotating member of the rotary machine, and the Ethernet data packets are sent from the transmitter to a primary winding mounted on the rotating member of the rotary machine. The Ethernet data packets are received at a secondary winding mounted to a stationary member of the rotary machine. The secondary winding is spaced apart from the primary winding by an air gap, and the secondary winding receives the Ethernet data packets via coupling between the primary and secondary windings. The Ethernet data packets are transmitted from the secondary winding to a receiver operatively connected to the secondary winding. 
     According to yet another embodiment of the invention, a system for providing communication between a rotating member and a stationary member in a rotary machine includes a power supply external to the rotary machine, a power transmission device mounted on the stationary member of the rotary machine and operatively connected to the power supply to receive power from the power supply, and a power receiving device mounted on the rotating member of the rotary machine. The power receiving device is operative to receive power from the power transmission device via contactless delivery of power. An electronic circuit mounted on the rotating member of the rotary machine receives power from the power receiving device. A transmitter configured to generate Ethernet data packets is operatively mounted in the electronic circuit. The system also includes a digital rotary transformer which has a primary side mounted to the rotating member of the rotary machine and a secondary side mounted to the stationary member of the rotary machine. The primary side of the digital rotary transformer is operatively connected to the transmitter to receive the Ethernet data packets, and the Ethernet data packets are transmitted between the primary side and the secondary side. A receiver is operatively connected to the secondary winding to receive the Ethernet data packets generated by the transmitter mounted on the rotating member of the rotary machine. 
     These and other advantages and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various exemplary embodiments of the subject matter disclosed herein are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
         FIG. 1  is a perspective view of an exemplary industrial control application incorporating the present invention; 
         FIG. 2  is a partial block diagram representation of the exemplary industrial control application of  FIG. 1   
         FIG. 3  is a partial sectional view of a motor according to one embodiment of the invention; 
         FIG. 4  is a schematic representation of a communication circuit between a rotating member of a motor and a motor drive according to one embodiment of the invention; 
         FIG. 5  is a partial sectional view of a motor incorporating one embodiment of a rotary coupler; 
         FIG. 6  is a partial sectional view of a motor incorporating another embodiment of a rotary coupler; and 
         FIG. 7  is a partial sectional view of a motor incorporating still another embodiment of a rotary coupler. 
     
    
    
     In describing the various embodiments of the invention which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word “connected,” “attached,” or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION 
     The various features and advantageous details of the subject matter disclosed herein are explained more fully with reference to the non-limiting embodiments described in detail in the following description. 
     The subject matter disclosed herein describes a contactless Ethernet communication technique adapted for communication between a rotor and a stator in a rotating machine. Power is supplied to the rotor via a contactless power transfer system. A transmitter on the rotating machine generates data packets in an industrial protocol, such as EtherNet/IP, for transmission on an Ethernet physical link layer. A rotary coupler is provided between the rotor and stator, where a rotating member on the rotor is communicatively coupled to a stationary member on the stator. The rotary coupler may include, for example, a digital rotary transformer. The data packet is transmitted in the industrial protocol via the rotary coupler. A receiver on the stationary side may receive the data packet where some initial processing may be performed and the data retransmitted. Alternately, a network device, such as a gateway, router, or switch may receive the data packet and pass it along the industrial network to a remote device for further processing. 
     Turning initially to  FIG. 1 , an exemplary industrial control system includes an industrial controller  10  in communication with a motor drive  30  and a remote processing device  20 . As illustrated, the industrial controller  10  is modular and may be made up of numerous different modules connected together in a rack or mounted to a rail. Additional modules may be added or existing modules removed and the industrial controller  10  reconfigured to accommodate the new configuration. Optionally, the industrial controller  10  may have a predetermined and fixed configuration. In the illustrated embodiment, the industrial controller  10  includes a power supply module  12 , a processor module  14 , a network module  16 , and two additional modules  18  that may be selected according to the application requirements and may be, for example, analog or digital input or output modules. 
     One or more remote processing devices  20  may be connected to the industrial control network. The remote processing device may be an operator interface located proximate to the industrial controller, a desktop computer located at a separate facility from the industrial controller, or a combination thereof. The remote processing device  20  may include a processing unit  22 , input device  24 , including, but not limited to, a keyboard, touchpad, mouse, trackball, or touch screen, and a display device  26 . It is contemplated that each component of the remote processing device may be incorporated into a single unit, such as an industrial computer, laptop, or tablet computer. It is further contemplated that multiple display devices  26  and/or multiple input devices  24  may be distributed about the controlled machine or process and connected to one or more processing units  22 . The remote processing device  20  may be used to display operating parameters and/or conditions of the controlled machine or process, receive commands from the operator, or change and/or load a control program or configuration parameters. An interface cable  28  connects the remote processing device  20  to the industrial controller  10 . 
     The industrial controller  10  is connected to other devices by one or more networks according to the application requirements. As illustrated, interface cables  28 ,  32  connect the industrial controller  10  to the remote processing device  20  and the motor drive  30 , respectively. It is contemplated that the interfaces cables  28 ,  32  may be a custom cable configured to communicate via a proprietary interface or may be any standard industrial network cable, including, but not limited to, EtherNet/IP, DeviceNet, or ControlNet. The network module  16  is configured to communicate according to the protocol of the network to which it is connected and may be further configured to translate messages between two different network protocols. An additional network cable  11  may be a standard Ethernet cable connected to a network external from the industrial network, such as the Internet or an intranet. 
     The industrial control network further includes a motor drive  30  and a motor  50 . The motor drive  30  is connected to the industrial controller  10  via a network cable  32 . As illustrated, the motor drive  30  is connected to a network module  16  to receive communications from the industrial controller  10 . The communications may include configuration packets or operating commands generated by the processing module  14 . Optionally, the industrial controller  10  may include another module (not shown) dedicated to communicating with the motor drive  30 . The additional module may be, for example, a servo module, which is configured to generate motion profiles, velocity profiles, or other command profiles and transmit the commands to the motor drive  30 . 
     The motor drive  30  receives the commands, which indicate a desired operation of the motor  50 , and generate a variable frequency and variable amplitude voltage for the motor to achieve the desired operation. A power cable  57  extends between the motor drive  30  and a junction box  59  on the motor to supply the variable frequency and variable amplitude voltage to the motor. A communication cable  62  extends between a first communication interface  64  (see also  FIG. 2 ) in the motor drive  30  and a second communication interface in the motor  50 . An encoder  60  is mounted to the rear of the motor  50  and generates a position feedback signal corresponding to an angular position of the motor  50 . The position feedback signal may be provided directly to the motor drive via a dedicated position feedback cable (not shown) or, optionally, the position feedback signal may be transmitted via the communication cable  62  to the motor drive  30 . The position feedback signal may be transmitted directly or after some initial processing, such as inserting the position information into a data packet for serial communications or converting the position signal to a velocity signal, is performed within the encoder  60  prior to sending the feedback signal to the motor drive  30 . Optionally, the communication interface within the motor  50  may be integrated within the encoder  60 . The position feedback information and additional data provided from a circuit within the motor  50  to the encoder  60  may be combined into a data packet by the encoder  60  for transmission to the motor drive  30 . The illustrated embodiment further includes a brake module  58  mounted between the motor  50  and the encoder  60 . A control signal is provided from an output  44  (see  FIG. 2 ) of the motor drive  30  to release the brake and a feedback signal may be provided from the brake  58  to the motor drive  30  to indicate the brake is opened. With reference also to  FIGS. 5 and 6 , it is contemplated that the brake  58  may be a disc brake system in which a rotating disc  82  is mounted to the drive shaft  56 . Calipers squeeze pads  84  together on each side of the rotating disc  82  to hold the disc in position, and the control signal is used to open the caliper, releasing the brake when motion is desired. 
     It is further contemplated that other sensors and/or actuators may be mounted to or within an extension of the housing for the motor  50  according to application requirements. For example, sensors such as a vibration sensor or a temperature sensor may be mounted at various locations within, on, or proximate to the housing of the motor  50  to monitor operating performance. Each of the sensors generates a signal that may be transmitted directly to the motor drive  30  or to an additional control module embedded within the housing of the motor  50 . The additional control module may include, for example, logic circuits such as analog to digital converters, buffers, processors and the like to receive the signals from each sensor and to convert the signals to another format and/or to provide data for the communication interface for insertion into data packets which are transmitted to the motor drive  30 . Additional conductors and/or cables may be connected between the motor drive  30  and the motor  50  according to the application requirements to transfer each of the control, communication, and/or feedback signals between the motor drive  30  and the motor  50 . 
     Referring next to  FIG. 2 , a portion of the exemplary industrial control system shown in  FIG. 1  is illustrated in block diagram form. Each of the modules  14 ,  16 ,  18  in the industrial controller  10  may include a processing device and memory. The functionality and size of the processing device and memory may vary according to the requirements of each module. As illustrated, each module  14 ,  16 ,  18  includes a processor  15 ,  17 ,  19  configured to execute instructions and to access or store operating data and/or configuration parameters stored in the corresponding memory device  21 ,  23 ,  25 . The processors  15 ,  17 ,  19  may be any suitable processor according to the module requirements. It is contemplated that processors  15 ,  17 ,  19  may include a single processing device or multiple processing devices executing in parallel and may be implemented in separate electronic devices or incorporated on a single electronic device, such as a microprocessor, a field programmable gate array (FPGA) or application specific integrated circuit (ASIC). Similarly, the memory devices  21 ,  23 ,  25  may be a single device, multiple devices or may be incorporated in part or in whole within the FPGA or ASIC. 
     The modules may further include additional logic and/or control circuits according to the module requirements. Each I/O module  18 , for example, includes input and/or output terminals and the associated circuitry  29  to connect the I/O module to an external device. The network module  16  includes a network interface  27  configured to receive data packets from the network media connected to the interface. According to the illustrated embodiment, the network interface  27  is connected to an external network via Ethernet cable  1 I as well as the motor drive  30  and remote processing device  20  via the respective network cables  32 ,  28 . The network module  16  may be configured to function as a gateway between networks and to convert data packets between protocols. 
     The motor drive  30  also includes a processing device and memory. As illustrated, the motor drive  30  includes a processor  36  configured to execute instructions and to access or store operating data and/or configuration parameters stored in the corresponding memory device  38 . The processor  36  may be any suitable processor according to the module requirements. It is contemplated that processor  36  may include a single processing device or multiple processing devices executing in parallel and may be implemented in separate electronic devices or incorporated on a single electronic device, such as a microprocessor, a field programmable gate array (FPGA) or application specific integrated circuit (ASIC). Similarly, the memory devices  38  may be a single device, multiple devices or may be incorporated in part or in whole within the FPGA or ASIC. The motor drive  30  also includes a network interface  34  to communicate with the industrial controller  10  and/or other devices via the industrial network. A feedback circuit  42  is in communication with the communication interface  64  and receives position feedback information from the encoder  60  which is transmitted via the communication cable  62 . The motor drive also includes a power section  40 , where the power section  40  is configured to receive either AC or DC power from an external source and convert the external power to the variable frequency and variable amplitude voltage supplied to the motor. The variable frequency and variable amplitude voltage is provided to a stator  52  of the motor  50  which causes the rotor  54  and, in turn, the drive shaft  56  of the motor to rotate. 
     The drive shaft  56  may be a single shaft extending through the rotor  54  and protruding from one end or both ends based on the configuration of the motor  50 . Optionally, the drive shaft  56  may include a first shaft portion extending from the front of the motor  50  and a second shaft portion extending toward the rear of the motor  50 . According to still another embodiment, illustrated in  FIG. 7 , the drive shaft  56  may include a first shaft portion extending from the front of the motor  56 , a second shaft portion  56  extending internally toward the rear of the motor, and a third shaft portion  71  coupled to the second shaft portion  56 . The second shaft portion is sized appropriately to be coupled to the disc  82  within the brake  58  and the third shaft portion is sized to extend through the encoder  60  and to receive the digital rotary transformer  70  on the reverse side of the encoder  60 . In any of the configurations described above, the drive shaft  56  or portions of the drive shaft rotate responsive to the variable frequency and variable amplitude voltage provided to the stator  52 . The portion of the drive shaft  56  extending from the front of the motor  50  may be coupled to and control operation of a machine, gearbox, or the like that is mechanically coupled to the drive shaft  56 . The portion of the drive shaft  56  extending toward the rear of the motor  50  may be coupled to the motor brake  58  and to a digital rotary transformer  70  as will be discussed in more detail below. The illustrated embodiment is intended to be exemplary and will be used herein for discussion purposes. It is understood that the drive shaft  56  may extend from just one side of the rotor  54  and be of sufficient length such that the motor brake and/or the digital rotary transformer  70  may be coupled to the same portion of the drive shaft  56  extending from the motor and coupled to a machine, gearbox, or the like. Further, the diameter of the drive shaft  56  may be uniform throughout its length or be varied according to the requirements of the device coupled to the drive shaft  56 . As also illustrated in  FIG. 7 , the drive shaft may include multiple portions coupled together either directly or indirectly, for example, via gears. For purposes of discussion herein, it is contemplated that the drive shaft  56  includes one or more members that cause rotation of a primary winding  72  for the digital rotary transformer  70  in tandem with rotation of the rotating member of the motor  50 . 
     In addition to causing rotation of the rotor and drive shaft within the motor  50 , the variable frequency and variable amplitude voltage may be utilized to transfer power from the stator  52  to a circuit mounted on the rotor  54 . Turning next to  FIG. 3 , a sectional view of a permanent magnet (PM) motor is shown as one embodiment of a synchronous motor controlled by the motor drive  30 . The PM motor  50  includes a rotor  54  having a number of poles  65 A,  65 B and a stator  52  having a number of windings  55 A- 55 C. For ease of illustration, one quarter of the motor is shown. The full PM motor  50  includes twelve windings  55  and eight poles  65 . As is understood in the art, each winding  55 A- 55 C is wound around a tooth  51 A- 51 C with the windings filling slots  53 A- 53 C between adjacent teeth  51 A- 51 C. Each winding  55 A- 55 C consists of a number of turns, N, wrapped around the tooth  51 A- 51 C. The PM motor  50  shown in  FIG. 3  is an interior permanent magnet motor, and each pole  65 A,  65 B includes a v-shaped slot in which a pair of magnets  61 A,  61 B is inserted, where one magnet of the pair is inserted into each leg of the v-shaped slot. Optionally, each pole  65 A,  65 B may include a bar magnet and a single slot. It is contemplated that the slots may take various other shapes and be configured to receive magnets  61  having a complementary shape to be inserted within the slot without deviating from the scope of the invention. 
     Each slot also includes a portion of a pick-up coil  63  located within the slot. According to the illustrated embodiment, each pick-up coil  63 A,  63 B is wound at the end of each v-shaped slot between the magnet  61 A,  61 B and the outer periphery of the rotor  54 . Each pick-up coil  63 A,  63 B may have a number of turns, where the coil is would in one direction through one end of the v-shaped slot, wound in the other direction through the other end of the v-shaped slot, and includes end-turns at each end of the rotor  54 . Optionally, the rotor  54  may include a first slot in which the magnet  61  is inserted and a second slot configured to receive the pick-up coil  63 . According to another embodiment, the rotor  54  may include a number of grooves or channels extending longitudinally along the length of the rotor  54  in which each of the pick-up coils  63  is received. 
     In operation, the motor drive  30  receives a reference signal, such as a speed reference, position reference, or a torque reference corresponding to desired operation of the motor  50  and regulates the amplitude and frequency of current and/or voltage supplied to the motor  50  to achieve the desired operation of the motor  50 . In one embodiment of the invention, the power section  40  of the motor drive  30  includes a current regulator module (not shown) to control the current provided to the motor  50 . The power section  40  uses the current values measured at the output of the motor drive  30  by current sensors. As is understood in the art, Park&#39;s transformation may be used to convert measured three-phase currents into a two-phase representation of the current along a quadrature axis (q-axis) and along a direct axis (d-axis). The q-axis current corresponds to the amount of torque produced by the motor  50  and the d-axis current corresponds to the flux established between the rotor  54  and the stator  52  in the motor  50 . The magnitude of flux is a function of the field strength of the permanent magnets  61  in the rotor  54 , of the windings  55  in the stator  52 , and of the tooth  51  and/or slot  53  shape in the stator  52 . 
     The current supplied to the stator  52  of the motor  50  from the motor drive  30  includes both fundamental and harmonic components. The fundamental component is the primary work producing component and, ideally, is the only component present to cause rotation of the rotor  54 . The frequency of the fundamental component of current applied to the motor  50  determines the speed at which the motor rotates. The fundamental current in the stator winding  55  generates a rotating electromagnetic field within the motor, where the speed at which the electromagnetic field rotates around the motor is a function of the frequency of the current and of the number of poles within the motor. The magnets  61  in the rotor  54  of the motor  50  establish a constant magnetic field. The rotating electromagnetic field resulting from the fundamental current applied to the stator interacts with the constant magnetic field of the rotor to cause rotation of the motor. 
     Harmonic components present in the current waveform are a result of modulation techniques used to generate the variable amplitude and variable frequency voltage output from the motor drive  30 . While the speed of the motor  50  is controlled by the fundamental component of the current, the harmonic components also effect operation of the motor  50 . The harmonic components generate a ripple current present on top of the fundamental component and cause undesirable power losses within the motor  50 . Each component of the current (i.e., fundamental and harmonic) create rotating electromagnetic fields within the motor  50  as a function of the frequency of the respective component. Because the amplitude of the fundamental component is significantly greater than the amplitude of any of the harmonic components, the rotating electromagnetic field generated by the fundamental component dominates performance and engages the magnetic field produced by the magnets  61  to control operation of the motor. The other rotating electromagnetic fields, however, still exert a force on the magnetic field produced by the magnets  61  and can cause a ripple torque on the rotor  54  corresponding to the ripple current observed on the current waveform. Additionally, the rotating electromagnetic fields of the harmonic components may establish eddy currents in the magnets  61  themselves, which, in turn, are dissipated as heat losses in the magnets. 
     The pick-up coil(s)  63  mounted to the rotor  54  reduces the ripple current and eddy currents generated by the harmonic components in the current. When a coil is present in a rotating electromagnetic field, a voltage is induced in the coil. Because the rotor  54  rotates synchronously with the fundamental component of the current, the pick-up coil  63  mounted to the rotor  54  experiences no rotational electromagnetic field from the fundamental component. The electromagnetic fields generated by the harmonic components, however, rotate at frequencies other than the fundamental frequency, and the pick-up coil(s)  63  mounted to the rotor experiences a rotating electromagnetic field, where the frequency of rotation of the rotating electromagnetic field, as experienced by the pick-up coil(s) is the difference between the frequency of the harmonic component and the fundamental component. These rotating electromagnetic fields experienced by the pick-up coil(s)  63  induce a voltage in the pick-up coil. This voltage induced in the pick-up coil results in wireless, or contactless, power transfer from the stator  52  to the rotor  54  and may be used to supply power to a circuit mounted on the rotor  54 . 
     With reference also to  FIGS. 5 and 6 , a capacitive element  78  may be operatively connected to the pick-up coil  63 . The capacitive element  78  may be a single capacitor or multiple capacitors connected in series, parallel, or a combination thereof. The inductive nature of the pick-up coil  63  in combination with the capacitive element  78  forms an L-C circuit. The inductance and capacitance values may be selected to establish a resonance in the L-C circuit at a frequency that is coincident with the frequency of one of the harmonic components. The resonance will increase the efficiency and capacity of power transfer between the electromagnetic field established by the corresponding harmonic component and the pick-up coil  63 . Optionally, an additional inductor may also be connected with the pick-up coil  63  and the capacitive element  78  to obtain a desired resonance from the L-C circuit. Selecting the capacitor and/or inductive values to coincide with a resonant operating point of the L-C circuit, increases the capacity of power transfer from the electromagnetic field established by the corresponding harmonic component to the pick-up coil  63 . 
     Turning next to  FIG. 4 , a schematic representation of a communication circuit between a rotating member of the motor  50  and the motor drive  30  is illustrated. The left portion of the illustrated communication circuit is mounted on the motor  50  and is one example of a circuit mounted to the rotor  54  which may receive power from the pick-up coil(s)  63 . A circuit board  76  includes a processor  90  and a memory device  92  mounted to the board. The processor  90  may be any suitable processor according to the module requirements. It is contemplated that processor  90  may include a single processing device or multiple processing devices executing in parallel and may be implemented in separate electronic devices or incorporated on a single electronic device, such as a microprocessor, a field programmable gate array (FPGA) or application specific integrated circuit (ASIC). Similarly, the memory device  92  may be a single device, multiple devices or may be incorporated in part or in whole within the FPGA or ASIC. With reference also to  FIGS. 5 and 6 , it is contemplated that the circuit board  76  may be circular and include an opening extending through the center of the board such that the circuit board  76  may be mounted on the drive shaft  56 . The circuit board  76  further includes a dedicated logic circuit  94  which includes components required to implement the physical layer of an Ethernet communication interface. 
     A digital rotary transformer  70  is mounted between the circuit board  76  and an Ethernet plug  81  on the motor  50 . The digital rotary transformer  70  includes a primary winding  72  and a secondary winding  74 . The primary winding  72  may be mounted on or adjacent to the circuit board  76 . The primary winding  72  rotates with the rotor  54  and receives the Ethernet data packets from the dedicated logic circuit  94 . With reference first to  FIG. 5 , the digital rotary transformer  70  includes a primary winding  72  and a secondary winding  74  mounted in planes adjacent to each other. An air gap exists between the windings, and the secondary winding  74  is mounted to a stationary feature within the motor such as the brake housing or to the interior of the motor housing. With reference next to  FIG. 6 , the digital rotary transformer  70  includes a primary winding  72  and a secondary winding  74  mounted coaxial to each other. An air gap is again present between windings, and the secondary winding  74  may be mounted to the stator  52  or interior housing of the motor. In either configuration, the primary winding  72  rotates with the rotor  54 , and the Ethernet data packet is transmitted to the primary winding. The high frequency data of the Ethernet data packet is transmitted between the primary and secondary windings and conducted to the plug  81  on the motor  50 . 
     The plugs  81 ,  83  on the motor  50  and motor drive  30  are preferably a standard Ethernet plug joined by a standard Ethernet cable  62 . The type of plug and cable selected may be according to the application requirements. The plugs  81 ,  83  may be, for example, an RJ45 connector or an M12 connector. The cable may be a CAT-5, CAT-6, or CAT-7 cable. According to still another embodiment of the invention, a proprietary plug and cable configuration may be implemented without deviating from the scope of the invention. The plugs  81 ,  83  and cable  62  establish an Ethernet network between the motor  50  and the motor drive  30 , delivering the Ethernet data packets generated on the rotor  54  of the motor. 
     Within the motor drive  30 , the communication interface  64  may include a stationary digital transformer  100  to provide isolation for the physical layer circuit  102  within the motor drive. The communication interface  64  receives the Ethernet data packets and may transfer the data packets or perform some initial processing of the data packets and transmit data from the payload of the data packet to the feedback circuit  42  or to the processor  36  within the motor drive  30  for subsequent use. 
     According to another aspect of the invention, the processor  36  in the motor drive  30  may also be configured to transmit data to the processor  90  on the rotating member of the motor  50 . Communication, as described above, from the rotating member of the motor  50  to the motor drive  30  may be bi-directional. Ethernet data packets may be transmitted in either direction across the digital rotary transformer  70 . 
     It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. 
     In the preceding specification, various embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.