Reluctance sensor for detection of position of a rotor in an electric machine

An electric machine includes at least a printed circuit board and a magnetically permeable element. The printed circuit board includes a reluctance coil configured to generate a voltage in presence of a magnetic flux. The magnetically permeable element has a first end positioned adjacent to a rotor of the electrical machine and a second end positioned adjacent to the coil of the printed circuit board. In some examples, rotation of the rotor causes a change in the magnetic flux through the magnetically permeable element and generation of the voltage across the reluctance coil.

TECHNICAL FIELD

This disclosure relates in general to the field of electric machines including motors and generators, and in particular, the detection of position of a rotor in an electric machine. Example electric machines include DC motors and generators, alternators and synchronous motors, and induction motors or asynchronous machines. The electric machines include a rotating part, referred to as the rotor, and a stationary part, referred to as the stator. Control of the electric machine may require, or otherwise be improved by, detection of the relative positions of the rotor and the stator.

DETAILED DESCRIPTION

An electric machine may be an electromagnetic rotating machine that includes a rotor and a stator. The rotor and stator are positioned on opposite sides of an air gap through which a magnetic field is present and magnetic flux flows between the rotor and the stator. The magnetic field may be created by permanent magnets or by current flowing in a winding. While other examples are possible, the electric machine may be a motor or a generator. The generator, which may be referred to as an engine-generator set or a genset, may include a power source (e.g., an engine) and an alternator or another device for generating electrical energy or power from mechanical energy. The motor, on the other hand, receives electrical energy and converts it to mechanical energy by outputting torque.

Controlling an electrical machine often requires feedback of absolute or relative position of the rotating element, called the rotor. This position is often measured using a position sensor. The position sensor can utilize a variety of different techniques, such as mechanical sensors, mechanical commutators, optical sensors, variable reluctance sensors, and hall effect sensors. Electrical machines are often coupled to engines. In this case, the engine is often controlled by an engine control unit (ECU). The ECU often requires engine position information for appropriate sequencing of certain engine actuators, such as fuel injectors, ignition devices, emissions control devices, protective functions, or control of the engine speed.

The following embodiments include a rotor position sensing system based on a magnetic field and/or reluctance caused by the rotation of the rotor of the electric machine. In one example, the rotor of the electric machine includes rotor teeth (extension of steel or other metal) and slots (absence of steel or other metal) between the rotor teeth. A printed circuit board (PCB) includes a sensing coil. A current or voltage generated in the sensing coil of the PCB may fluctuate according to the magnetic field or reluctance through the sensing coil. As the rotor teeth pass near the sensing coil, the magnetic field or reluctance is modified. A controller (e.g., ECU) may monitor and detect fluctuations in the generated current or voltage in order to determine how many teeth are passing the sensing coil and/or the speed at which the teeth are passing the sensing coil in order to determine the position and/or speed of the rotor. In one example, the PCB also includes the stator windings for the electrical machine. The PCB may include an outer portion (e.g., outside the magnetic portion of the rotor) including the sensing coil and an inner portion (e.g., adjacent to the magnetic portion of the rotor).

FIG.1illustrates an example electric machine including a rotor position detection system20and a stator implemented by PCB21arranged in cooperation with a rotor124including permanent magnets. The permanent magnets define a magnetic region where the flux from the magnets varies significantly while the rotor is rotating. The magnetic region may reside radially between an inner diameter of the magnets and an out diameter of the magnets. The magnetic region may extend slightly outside the region defined by the inner and outer diameter of the magnets. A sensing coil22is located outside of the magnetic region defined by the inner and outer diameter of the magnets. The sensing coil22may be a predetermined distance (e.g., 1 inch, 3 centimeters, 10 centimeters, or another value) outside of the magnetic region. The predetermined distance may be selected according to one or more factors. One example factor is based on a rotating feature such as the tooth or hole. For example, the predetermined distance may be based on the size of relative permeability of the tooth or hole. Another example factor is based on a stationary feature such as the permeable element. For example, the predetermined distance may be based on the size of relative permeability of the permeable element. One example factor is the length of magnetic path when permeable feature is present. One example factor is the length of magnetic path when permeable feature is not present. One example factor may include mechanical tolerances in the machine (such as end play or manufacturing tolerance).

The area outside the region defined by the inner and outer diameter of the magnets may be referred to as the non-magnetic region, periphery, or outer sensor region.

The stator is supported in a stator clamshell125which is connected to an engine block121. The rotor124is supported by bearings connecting it to the stator clamshell125and an engine crankshaft120. The printed circuit board may include coils of wire, or traces, that are energized in response to relative movement of magnets through electromagnetic induction. The coils may be included in different layers of the printed circuit board. Because the coils reside on the printed circuit board, the armature inductance (caused by the permeability of the iron used to direct the magnetic flux through the windings) may be lower, which may decrease the voltage drop under load, improve the efficiency of the generator and decrease the commutation losses in semiconductor diodes connected to rectify the output of the machine to direct current.

The shape of the windings may include concentric circles, rectangles, trapezoids to match magnet shape, or another shape. The exciter windings may be formed from copper or another conductive material. The traces may exist on multiple layers of the PCB. The traces forming the exciter windings are configured to induce a field current in response to magnetic fields of the stator magnets.

Although embodiments illustrated herein relate to an axial air gap electrical machine, embodiments are contemplated relating to a radial air gap electric machine, an engine, a driven component, such as a drive shaft, a fan, a propeller or similar driven component. In addition, the scope of the disclosure disclosed herein is not limited to position sensing for a rotating element. One skilled in the art can apply the concepts herein to any situation where a physical quantity may be measured based on the reluctance of a magnetic path. Examples include but are not limited to, linear position measurement, pressure measurement, sound measurement, temperature measurement, magnetic saturation level, allotrope characteristics, metallurgical characteristics, force measurement, and torque measurement.

FIG.2illustrates an example magnetic equivalent circuit10for the example rotor position sensing system20illustrated inFIGS.3and4. For the example magnetic equivalent circuit10, the current in the equivalent circuit10corresponds to the magnetic flux through the magnetic path12illustrated inFIGS.3and4. The current in the magnetic equivalent circuit10is related to the total magneto-motive force supplied to the circuit and the total equivalent resistance along the magnetic path, represented by the sum of Rg, R1, R2Ra1, and Ra2.

The example magnetic equivalent circuit10is supplied by a magneto-motive force (MMF) generated by a magnetic field generation device11. Typical examples of a magnetic field generating device11include an electrically conductive coil (e.g., one or more coil traces on a PCB), a single electrical conductor, a solenoid, a permanent magnet, and residual magnetism in a ferrous material, or others.

The resistance Rgcorresponds to the reluctance added to the magnetic circuit by the air gap29between a first permeable element23and a second permeable element24. The resistance R1corresponds to the reluctance added to the magnetic circuit by the first permeable element23. The resistance R2corresponds to the reluctance added to the magnetic circuit by the second permeable element24. The resistance Ra1corresponds to the reluctance added to the magnetic circuit by a first air gap25. The resistance Ra2corresponds to the reluctance added to the magnetic circuit by a second air gap26. The resistance Rrcorresponds to the reluctance added to the magnetic circuit by a ferrous rotating element27.

The rotating element27may include of multiple rotating elements connected by a magnetically permeable path, the rotating element27may include of a single rotating element. The rotating element27may have permanent magnets28connected to it by a securement device, such as an adhesive, a mechanical retainer, fusing of material, a weld, a press fit, a fastener, such as a screw, or another securement device. The permanent magnets28may be formed as a part of the rotating element. The permanent magnets28may be discrete pieces of permanent magnet material, such as a neodymium magnet or NdFeB, Samarium Cobalt, ferrite, ceramic, AlNiCo, or a different type of material. The permanent magnets may be locally magnetized portions of a disc composed of permanent magnet material.

The permanent magnets28may provide a magnetic flux that may flow through the printed circuit board21, potentially generating a voltage in windings distributed on the printed circuit board21. The voltage generated in windings distributed on the printed circuit board21may provide a substantial portion of the torque produced or consumed by an electrical machine. The rotor position detection system20may be used to determine a commutation time and sequence for current flowing in windings distributed on the printed circuit board21.

For each resistive element in the example magnetic equivalent circuit10, the reluctance is related to the length of the path and the relative permeability of the material though which the magnetic flux will pass. The relative permeability of ferrous materials may be significantly greater than the relative permeability of air, as an example, the relative permeability of silicon steel may be 5,000 or 10,000 time the permeability of air.

For the example rotor position sensing system20, the relative permeability of the first permeable element23, second permeable element24and ferrous rotating element27is approximately 6,000 times the permeability of air. Due to the geometry of the example rotor position sensing system20, Ra1and Ra2comprise about 70% of the reluctance in the magnetic circuit inFIG.3and about 93% of the reluctance of the magnetic circuit inFIG.4.

For the example rotor position sensing system20, the magnetic field generating device11is the coil22, comprised of traces on multiple layers of a printed circuit board (PCB). Due to magnetic induction, the voltage generated by the coil22is related to the rate of change of the magnetic flux through the coil. The magnetic flux through the coil depends on the current flowing through the coil22as well as the reluctance of the magnetic path12. With a constant current, the magnetic flux, and thereby the voltage, depends on the reluctance of the magnetic path12.

In addition, the inductance of a coil may be related to the magnetic path length for the flux flowing through the coil. The magnetic path length may be directly measured by directly measuring the inductance of the coil. The inductance of a coil may be measured by applying a voltage to the coil and monitoring the resulting behavior of the current. The voltage applied to the coil may be a time varying voltage. The resulting behavior of the current may be monitored for amplitude, rise rate, fall rate, phase shift, time constant, or other similar characteristics.

FIGS.5,6, and7illustrate additional example embodiments of rotor position sensing system20. In the example ofFIG.5, rotor position sensing system20may include a multi-element rotor with external teeth31, shown with teeth present in a first state32and teeth absent in a second state33.

FIG.6illustrates an example in which the rotor position sensing system20may include a single-element rotor with external teeth34, shown in a first state35with teeth present (in line with the sensor) and in a second state36with teeth absent (not in line with the sensor).FIG.7illustrates an example in which the rotor position sensing system20may include a multi-element rotor with position sensing holes37, shown with a hole out of alignment with the sensor in state38and hole in alignment with the sensor in state39.

The magnetic field generation device11may provide a constant magneto motive force by applying a constant direct current to coil of the rotor position sensing system20.FIG.8illustrates an example driving and filtering circuit to apply a constant direct current to coil of the rotor position sensing system20and to extract a meaningful signal indicating the rate of change in the magnetic flux through the magnetic path detected by the sensor. This signal may be further processed to provide a tooth indication signal.

In one example, the current to the coil of the rotor position sensing system20may be varied based on the speed of the rotating element (e.g., rotating element27). For example, the current amplitude or an excitation frequency may be varied in the AC drive case.

The driving and filtering circuit illustrated inFIG.8illustrates the coil providing the magneto-motive force to the magnetic equivalent circuit, such as the coil of the rotor position sensing system20, as inductive element40. The current through coil (inductive element40) is controlled by current source41to a constant target set by resistive divider42. The current source41may be an integrated circuit, a field effect transistor (FET) controlled by an Op-Amp, a bipolar junction transistor (BJT) controlled by an Op-amp, a BJT with compensated drive current, or another type of current source.

Changes in the magnetic path length for the flux flowing through the inductive element40may cause a voltage to be generated across inductive element40. This voltage may be limited by protective device43to prevent damage to the components of the current source41. Protective device43may be a Zener diode, gas discharge tube, varistor, avalanche diode, combination of such elements or other protective device. Protective device43may be omitted.

The decoupling capacitor44removes the DC component of the voltage across the inductive element40from the incoming signal45, potentially improving immunity to changes in the DC voltage across the inductive element40, which may be a result of temperature fluctuations, manufacturing tolerance, physical positioning environmental effects, or other factors that do not relate to the magnetic path length and are not desirable to measure. Embodiments are contemplated where the decoupling capacitor44is not included.

The comparison voltage46represents a threshold indicating a typical inductive element40voltage when resting. The comparison voltage46may be provided by a resistive divider or may be derived from the incoming signal45through a filter.

The overvoltage protection circuit47may act to prevent the incoming signal45from exceeding the allowable input limits for the comparator48. The protective elements in the overvoltage protection circuit47may be Zener diodes, rectifier diodes, Schottky diodes, varistors, gas discharger tubes, avalanche diodes, or another protective device. The overvoltage protection circuit47may be omitted if unnecessary under all operating conditions.

Based on the operation of the comparator48, the output signal49may represent a digital signal resulting from the analog incoming signal45for use by digital circuitry such as a logic device, a microprocessor, a microcontroller, a complex programmable logic device (CPLD), a field programmable gate array (FPGA), or another device that solves digital logic. Embodiments are contemplated where the incoming signal45is fed directly into an analog circuit device or converted to a digital signal using an analog to digital converter or similar device.

FIG.9illustrates example waveforms produced by the circuit illustrated inFIG.4when inductive element40represents the coil for the rotor position detection system20fromFIGS.3and4. Analog waveform50represents an example of incoming signal45. Digital waveform51illustrates an example of output signal49. Rotor tooth signal52illustrates presence of a tooth aligning with the first permeable element23and second permeable element24. Maximum alignment position53corresponds toFIG.3. Minimum alignment position54corresponds toFIG.4.

In most cases, a rotor position detection system20applying a constant magneto-motive force using a permanent magnet or a constant current through an inductive element40, such as the coil from the rotor position detection system20, may only detect position when the ferrous rotating element27is moving. When the ferrous rotating element27is stopped, the magnetic flux through the coil may remain substantially constant, likely resulting in a very small or zero rate of change for the flux, which may generate a very small or 0 voltage across the inductive element40.

The magnetic field generation device11may provide a time-varying magneto motive force by applying a time-varying current or a time varying voltage to coil22.FIGS.10and11illustrate an example driving and filtering circuit to apply a time-varying voltage to an inductive element60and to extract a meaningful signal indicating the length of the magnetic path for flux passing through the inductive element60, first permeable element23and second permeable element24. This signal may be further processed to provide a tooth indication signal.

The time varying drive circuit shown inFIGS.10and11contains an increasing current path (illustrated inFIGS.19-22) and a decreasing current path (illustrated inFIGS.23-30). The current63follows the increasing current path through the increasing current switches61, the inductive element60, and the current sensing resistor64when the increasing current switches61are active. The current63follows the decreasing current path through the alternate passive path components62and the inductive element60when the increasing current switches61are not active until the current63through the inductive element60reaches a lower threshold value, such as 0.

The increasing current switches61may be driven to switch at a frequency. This frequency may be a fixed frequency much greater than an intended measurement frequency, a variable frequency or another frequency. The increasing current switches may be driven at a 50% duty cycle, a duty cycle slightly less than 50% to prevent windup when a tooth is moving into alignment with the first permeable element23and the second permeable element24. The increasing current switches may be driven at a varying duty cycle or another duty cycle.

The increasing current switches61may be semiconductor switches, such as FETs, BJTs, insulated-gate bipolar transistors (IGBTs), or another semiconductor switch. The increasing current switches61may be other switches, such as MEMs switch elements, relays, contacts, or any other device capable of switching electrical current. The alternate passive path components62may be semiconductor devices, such as rectifier diodes, Schottky diodes, Zener diodes, avalanche diodes, or another passive electric current conductive element. The alternate passive path components may be a semiconductor switch, such as a FET, BJT or IGBT, or another current switching device.

When current flows through the increasing current path, this current will flow through current sensing resistor64. Current through current sensing resistor64will result in a voltage across the current sensing resistor64, proportional to the current through the current sensing resistor64. The voltage across current sensing resistor64may be filtered by a filter to provide a representative position waveform65.

One skilled in the art may see that the current sensing resistor64may be applied to any portion of the increasing or decreasing current path and still provide similar behavior. In addition, embodiments are contemplated where the current through the inductive element60is measured by a different current measurement technique, such as a closed-loop magnetic sensor, an open-loop magnet sensor, passive current sensing across one or more increasing current switch or other means of measuring current. In some cases, current sensing resistor may be omitted.

In addition, embodiments are contemplated where voltage is applied to the inductive element60using various circuit topologies. The embodiments disclosed herein may be driven by a wide variety of fixed and time-varying current or voltage sources.

FIGS.12and13illustrate an example waveform representing the current through the inductive element60where the inductive element60represents the coil of the rotor position detection system20represented by traces on a printed circuit board.FIG.12illustrates an example waveform representing the current through the inductive element60when the rotor is in the position illustrated byFIG.3.FIG.13illustrates an example waveform representing the current through the inductive element60when the rotor is in the position illustrated byFIG.4.

It is possible to determine the absence or presence of a tooth or hole based only on characteristics of the current through the inductive element60as sensed by current sensing resistor64in example system illustrated byFIGS.10and11. In this case, it may be possible to determine the position of the ferrous rotating element27without the need for movement of the ferrous rotating element. Such a possibility may provide enough benefit over a constant magneto-motive force rotor position sensing technique, such as that shown inFIG.8, to offset any drawbacks to a time-varying application of voltage or current, such as increased circuit cost, increase circuit control complexity, increased EMI consideration, or other drawback encountered when implementing a time-varying application of voltage or current, such as provided by the circuit illustrated inFIGS.10and11.

FIG.14illustrates example waveforms from a rotor position sensing system20where the inductive element60of the time-varying drive circuit ofFIGS.10and11and represents coil22on the printed circuit board21. Coil Current80illustrates the current through inductive element60, representing the current through coil22. Position Indication81represents the representative position waveform66output from the time varying drive circuit. Rotor tooth signal82illustrates presence of a tooth aligning with the first permeable element23and second permeable element24. Maximum alignment position83corresponds toFIG.3. Minimum alignment position84corresponds toFIG.4.

FIGS.15,16,17and18illustrate four positions of an example toothed wheel91as it moves past an example variable reluctance sensor92. The variable reluctance sensor92contains a coil93and is driven by a constant magneto-motive force, produced by a permanent magnet94.

For the example illustrated inFIG.15, the tooth95is in maximum alignment with the variable reluctance sensor92. The magnetic path length for flux through the coil93travels through the ferrous material of the tooth95and the magnetic flux is at a maximum because the reluctance is at a minimum.

For the example illustrated inFIG.16, the tooth95is traveling out of alignment with the variable reluctance sensor92. The magnetic path length for flux through the coil93travels through the ferrous material of the tooth95on one side, but mostly through free air on the other side. The magnetic flux is falling at a maximum rate because the tooth95is traveling away from the center of the variable reluctance sensor92.

For the example illustrated inFIG.17, the tooth95is at minimum alignment with the variable reluctance sensor92, while next tooth96begins to approach the variable reluctance sensor92. The magnetic path length for flux through the coil93travels through no ferrous material and the magnetic flux is at a minimum because the reluctance is at a maximum.

For the example illustrated inFIG.18, the next tooth96is beginning to come into alignment with the variable reluctance sensor92. The magnetic path length for flux through the coil93travels through the ferrous material of the next tooth96on one side, most mostly through free air on the other side. The magnetic flux is rising at a maximum rate because the tooth96is traveling toward the center of the variable reluctance sensor92.

FIGS.19,20,21and22illustrate four positions of an example toothed wheel101as it moves past an example variable reluctance sensor102. The variable reluctance sensor102is excited by a coil, similar to the coil of the rotor position detection system20.

For the example illustrated inFIG.19, the tooth105is in maximum alignment with the variable reluctance sensor102. The magnetic path length for flux through the coil travels through the ferrous material of the tooth105and the magnetic flux is at a maximum because the reluctance is at a minimum.

For the example illustrated inFIG.20, the tooth105is traveling out of alignment with the variable reluctance sensor102. The magnetic path length for flux through the coil travels through the ferrous material of the tooth105on one side, but mostly through free air on the other side. The magnetic flux is falling at a maximum rate because the tooth105is traveling away from the center of the variable reluctance sensor102.

For the example illustrated inFIG.21, the tooth105is at minimum alignment with the variable reluctance sensor102, while next tooth106begins to approach the variable reluctance sensor102. The magnetic path length for flux through the coil travels through no ferrous material and the magnetic flux is at a minimum because the reluctance is at a maximum.

For the example illustrated inFIG.22, the next tooth106is beginning to come into alignment with the variable reluctance sensor102. The magnetic path length for flux through the coil travels through the ferrous material of the next tooth106on one side, most mostly through free air on the other side. The magnetic flux is rising at a maximum rate because the tooth106is traveling toward the center of the variable reluctance sensor102.

FIGS.23-30illustrate four positions of an example drilled wheel111as it moves past an example variable reluctance sensor112. One position is illustrated by a front view ofFIG.23and side view ofFIG.24. One position is illustrated by a front view ofFIG.25and side view ofFIG.26. One position is illustrated by a front view ofFIG.27and side view ofFIG.28. One position is illustrated by a front view ofFIG.29and side view ofFIG.30.

InFIGS.23/24,25/26and27/28, the variable reluctance sensor112is excited by a coil, similar to the coil of the rotor position detection system20, contained in printed circuit board113. ForFIGS.29/30, the variable reluctance sensor112is excited by a coil114, wound around the permeable path for the sensor.

For the example illustrated inFIG.23, the hole115is in maximum alignment with the variable reluctance sensor112. The magnetic path length for flux through the coil travels through the ferrous material of the hole115and the magnetic flux is at a minimum because the reluctance is at a maximum.

For the example illustrated inFIG.25, the hole115is traveling out of alignment with the variable reluctance sensor112. The magnetic path length for flux through the coil travels through the ferrous material of the hole115on one side, but mostly through free air on the other side. The magnetic flux is rising at a maximum rate because the hole115is traveling away from the center of the variable reluctance sensor112.

For the example illustrated inFIG.27, the hole115is at minimum alignment with the variable reluctance sensor112, while next hole116begins to approach the variable reluctance sensor112. The magnetic path length for flux through the coil travels through no ferrous material and the magnetic flux is at a maximum because the reluctance is at a minimum.

For the example illustrated inFIG.29, the next hole116is beginning to come into alignment with the variable reluctance sensor112. The magnetic path length for flux through the coil travels through the ferrous material of the next hole116on one side, most mostly through free air on the other side. The magnetic flux is falling at a maximum rate because the next hole116is traveling toward the center of the variable reluctance sensor112.

FIG.31illustrates an example controller100, which may be applied as rotor position controller or reluctance sensing circuit. The controller may include a processor200, a memory201, and a communication interface203. The communication interface203may communicate with a parallel input signal210, a sensor input signal212, a display device214, and/or an input device204. Additional, different, or fewer components may be included.

FIG.32illustrates an example flow chart for operation of the controller100. Additional, different, or fewer components may be used.

At act S101, the controller100receives data indicative of a current generated by a reluctance sensor of the electric machine. The current may originate with a magnetic flux through a magnetically permeable element positioned in proximity to a rotor of an electric machine. The data may be a voltage value determined by a voltage sensor connected to a reluctance coil configured to receive the magnetic flux.

At act S103, the controller100performs a comparison of the data indicative of the current in the reluctance sensor to a threshold. The current generated by the reluctance sensor is proportional to the reluctance of a magnetic circuit including at least one air gap and at least one permeable element. The current generated by the reluctance sensor is proportional to the reluctance of a magnetic circuit including a first permeable element, a second permeable element, and an air gap and between the first permeable element and the second permeable element. The data indicative of the current in the reluctance sensor indicates a presence or absence of rotor teeth spaced apart on the rotor. The data indicative of the current in the reluctance sensor indicates a hole in the rotor and configured to affect magnetic flux to the reluctance.

At act S105, the controller100determines a speed of the rotor or a position of the rotor based on the comparison. The controller compares the data indicative of the voltage generated by the reluctance coil in order to estimate a position or speed of the rotor.

At act S107, the controller100generates a command for the rotor based on the detected speed of the rotor or position of the rotor. For example, the controller100may determine or identify a speed setting (e.g., constant speed) as a target for the speed of the rotor. In another example, the controller100may determine or identify a position setting as a target for the position of the rotor (e.g., stepper motor). In another example the controller100may determine a speed setting corresponding to a target output (e.g., target output frequency) of a generator. The engine driving the generator may operate at a variable speed with the output voltage controlled by adjusting the engine speed according to the speed setting based on feedback from the reluctance sensor and the controller100.

The processor200may include a general processor, digital signal processor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), analog circuit, digital circuit, combinations thereof, or other now known or later developed processor. The processor200may be a single device or combinations of devices, such as associated with a network, distributed processing, or cloud computing.

The memory201may be a volatile memory or a non-volatile memory. The memory201may include one or more of a read only memory (ROM), random access memory (RAM), a flash memory, an electronic erasable program read only memory (EEPROM), or other type of memory. The memory201may be removable from the network device, such as a secure digital (SD) memory card.

In addition to ingress ports and egress ports, the communication interface303may include any operable connection. An operable connection may be one in which signals, physical communications, and/or logical communications may be sent and/or received. An operable connection may include a physical interface, an electrical interface, and/or a data interface.