Method of determining a beat

Abstract

A method for determining runout error includes generating a first magnetic field to interact with a second magnetic field generated by four or more magnetic poles of a magnet ring mounted to a first platform. The interaction can cause the first platform to rotate relative to a second platform. The method can also include receiving data from a magnetic field sensor, the data including each boundary between adjacent ones of the four or more magnetic poles relative to a corresponding nominal boundary defined by a substantially uniform boundary spacing. The method can include determining a magnetic field pattern from the data, and determining an angular position of the four or more magnetic poles based on the pattern. The method can also include determining an angular difference between the determined angular position and a nominal angular position. The method can also include determining a runout error based on a magnitude of the angular difference.

Description

BACKGROUND

[0001] Rotary joint devices, such as rotary electric machines, are often used to transmit power and / or electrical signals between one structure and another in electromechanical systems that operate by causing relative rotation between the two structures (e.g., a stator and a rotor). Example systems that employ rotary joint devices include remote sensing systems (e.g., RADAR, LIDAR, etc.) and robotic systems (e.g., for directing microphones, speakers, robotic components, etc.) among others. Rotary joint devices can also include a stator and a ring of magnets on a rotor. The spacing between the magnets on the rotor can be “dithered” to provide a unique fingerprint that can be used to determine the angular position of the electric machine. However, changes in environmental conditions can affect the unique fingerprint readout. These changes can affect the accuracy of determining the angular position of the electric machine. SUMMARY

[0002] The present disclosure generally relates to measuring mechanical runout and compensating for runout-associated encoder errors in rotary joint devices, such as brushless DC electric machines. In particular, a processing system can detect a signal as a rotor rotates relative to a stator. Any changes in the signal can indicate a runout error. Based on determining and measuring the runout component in the signal, the runout component of the signal can then be removed to improve accuracy. By extracting the changes attributable to runout, the present disclosure can provide a method to address unforeseen changes in the mechanical system of a brushless DC electric machine. For example, electric machine bearing health issues or encoder errors from dynamic loads. The correction can also serve as a way to improve calibration of a brushless DC electric machine.

[0003] In one aspect, the present application describes generating a first magnetic field that interacts with a second magnetic field generated by four or more magnetic poles of a magnet ring mounted to a first platform. The magnetic fields can cause the first platform to rotate relative to a second platform about an axis of rotation. The present application also describes receiving, from a magnetic field sensor connected to the second platform, data indicative of a characteristic of the second magnetic field. The characteristic of the second magnetic field can reflect a shift of each respective boundary between adjacent ones of the four or more magnetic poles relative to a corresponding nominal boundary defined by a substantially uniform spacing of boundaries of the four or more magnetic poles about the magnet ring. The present application also describes determining a magnetic field pattern based on the data received from the magnetic field sensor. Based on the magnetic field pattern, the present application describes determining an angular position of the four or more magnetic poles of the magnet ring relative to the first platform. An angular difference between the angular position of the four or more magnetic poles of the magnet ring relative to the first platform and a nominal angular position defined by the substantially uniform spacing of boundaries of the four or more magnetic poles about the magnet ring can also be determined. The determined angular difference can then be plotted. Finally, based on a magnitude of the plotted angular difference, a runout error can be determined.

[0004] In another aspect, the present application describes a method of mitigating encoder errors in a brushless DC motor. The method can include generating a first magnetic field that interacts with a second magnetic field generated by four or more magnetic poles of a magnet ring mounted to a first platform such that the first platform rotates relative to a second platform about an axis of rotation. The method can also include receiving data indicative of a feature of the second magnetic field from a magnetic field sensor connected to the second platform. The data can include a shift of each respective boundary between adjacent ones of the four or more magnetic poles relative to a corresponding nominal boundary defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles about the magnet ring. Based on the data received from the magnetic field sensor, the method can include determining a signal defined by an angular position of the four or more magnetic poles of the magnet ring relative to the second platform. The method can also include determining a difference signal between the signal defined by the angular position of the four or more magnetic poles of the magnet ring relative to the second platform and a nominal signal defined by the substantially uniform spacing of the boundaries of the four or more magnetic poles about the magnet ring. The method can then include measuring a sinusoidal component and removing the sinusoidal component from the difference signal to determine a phase fingerprint signal. Finally, the method can include determining a position of the magnetic poles of the magnet ring on the first platform based on the phase fingerprint signal. The position can include a spacing between the boundaries between adjacent ones of the four or more magnetic poles.

[0005] In another aspect, the present application also describes an electric motor. The electric motor can include a magnet ring comprising four or more magnetized poles mounted to a first platform, and a plurality of magnetic field sensors connected to a second platform. The second platform can rotate relative to the first platform about an axis. Further, during rotation, the plurality of magnetic field sensors can output signals used to generate a run-out corrected fingerprint associated with the electric motor.

[0006] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a simplified block diagram of an apparatus including a rotary joint according to example embodiments.

[0008] Figure 2 shows a side view of an apparatus including a rotary joint according to example embodiments.

[0009] Figure 3 shows a magnet ring according to example embodiments.

[0010] Figure 4 shows a magnet ring and magnetic field sensors according to example embodiments.

[0011] Figure 5A A positive angular error due to runout is shown in accordance with example embodiments.

[0012] Figure 5B A negative angular error due to runout is shown in accordance with example embodiments.

[0013] Figure 6 A flowchart in accordance with example embodiments is shown.

[0014] Figure 7A A plot of angular difference with runout in accordance with example embodiments is shown.

[0015] Figure 7B A plot of calibrated angular difference without runout in accordance with example embodiments is shown.

[0016] Figure 8 A flowchart in accordance with example embodiments is shown. DETAILED DESCRIPTION

[0017] Example methods, devices, and systems are described herein. It should be understood that the words “example” and “exemplary” are used herein to mean “serving as an example, instance, or illustration.” Any implementation or feature described herein as “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations or features. Other implementations can be utilized, and other changes can be made, without departing from the scope of subject matter presented herein.

[0018] Accordingly, the example embodiments described herein are not meant to be limiting. It will be readily understood to those skilled in the art that the aspects of the present disclosure as generally described herein and illustrated in the figures can be arranged, substituted, combined, separated, and designed in various different configurations.

[0019] Throughout the description, the article “a” is used to introduce an element of example embodiments. Any reference to “a” is to be read as meaning “at least one” and any reference to “the” is to be read as meaning “the at least one” unless otherwise indicated or unless the context clearly dictates otherwise. The use of the conjunctive “or” in the context of described lists of items is intended to mean any of the listed terms or any combination of the listed terms.

[0020] The use of ordinal numbers such as “first,” “second,” “third,” etc. is used to distinguish elements and not to denote a particular order. For the purpose of description, the terms “a number of” and “a plurality of” mean “two or more” or “more than one.”

[0021] Furthermore, the features shown in each figure can be used in combination with each other, unless the context clearly dictates otherwise. Thus, the appended drawings are to be considered in all Figure 1Generally, the nomenclature used herein, as well as the nomenclature used throughout the disclosure, is intended to be consistent with the nomenclature set out in the American Chemical Society publication, Nomenclature of Organic Chemistry, Elements of

[0022] Furthermore, any enumeration of elements, blocks, or steps in the present specification or claims is done for clarity. As such, such enumeration should not be construed to require or imply that these elements, blocks, or steps must follow a certain arrangement or be executed in a certain order.

[0023] I. SUMMARY

[0024] Many automotive, robotic, and industrial devices include components that rotate relative to one another. Brushless DC electric machines are one example of devices that include components that rotate relative to one another. Such components can be included on or themselves form two platforms that are rotationally coupled to one another. An example of a two-sided brushless DC electric machine can include two platforms arranged a predetermined distance apart from one another. In one example, the two platforms can include circular disks arranged concentrically about a common axis of the respective disks to maintain overlap between the two platforms in response to rotation of either of the two platforms about the common axis.

[0025] In some cases, the angular position of the first platform relative to the second platform can be of interest. For example, when tracked over time, the angular position can be used to determine and track the relative displacement between the first and second platforms. In another example, the angular position can be used to control an appendage of a robotic device, to guide or manipulate a sensor or other component on an automobile, or to otherwise position a rotational joint. In, for example, a brushless DC electric machine, a ring of magnets having wobbled poles can be mounted to the first platform. The wobbled poles can cause the electric machine to function as an absolute encoder. The angular spacing of the poles on the platform can be measured by one or more magnetic field sensors mounted to the second platform and used to determine the angular position of the poles on the platform. This angular position of the poles can also be used to determine the position of one platform relative to the other. The angular position can help monitor the health of the rotational joint device and help determine manufacturer differences.

[0026] The magnet ring can be mounted about an axis of rotation of the two platforms. The boundaries between each two adjacent magnetic poles can be dithered (e.g., shifted) relative to the corresponding nominal boundaries of the two adjacent magnetic poles. The nominal boundaries can be reference points defined by a substantially uniform spacing of the magnetic pole boundaries about the circumference of the magnet ring. Thus, the dithered magnetic poles can be formed by four or more magnetic poles having different sizes, resulting in boundaries between the magnetic poles being shifted relative to where the boundaries would be if each magnetic pole had the same size.

[0027] The shifted magnetic pole boundaries can define a characteristic dither pattern of the magnet ring. The characteristic dither pattern can be known to a control system or circuit used in association with the magnet ring, and can be used as a reference to determine the rotational position of the magnet ring. That is, one or more magnetic field sensors can be used to measure the magnetic field pattern of the magnet ring during its rotation. The measured magnetic field pattern, or aspects thereof, can be correlated (e.g., cross-correlated) with the characteristic dither pattern to determine a shift between the measured pattern and the characteristic pattern. The shift between the measured pattern and the characteristic pattern can be indicative of the relative position of the magnet ring at different points during the measurement relative to the sensor. That is, the shift can identify which magnetic poles are associated with the measured magnetic field pattern based on the characteristic dither pattern.

[0028] However, external factors can cause errors in detecting the measured magnetic field pattern. For example, manufacturer errors or runout in positioning the magnetic poles can erroneously affect the detected magnetic field pattern. If the measured shifted magnetic pole boundaries of the magnet ring are different from the actual boundaries in the characteristic dither pattern, the correlation and shift between the measured pattern and the characteristic pattern can not be accurately calculated. Thus, the angular position and the relative position of the magnet ring can not be reliably determined.

[0029] Some errors, such as manufacturer errors, can be corrected through calibration. However, runout is typically an error that is not mitigated through pre-operation calibration. Variations in environmental or load conditions during operation, such as temperature, wind speed, acceleration, and braking, are typical factors that contribute to causing runout. Runout affects the accuracy of the magnetic field sensor data when the shafts of the support platforms are not rotating in perfect unison with the common axis of rotation. When the shafts are not rotating in unison with the common axis of rotation, the magnetic field sensors can detect the position of the magnetic poles in an incorrect position. Thus, runout can negatively affect the determination of the angular position of the magnetic poles.

[0030] In an example embodiment, the runout error can be measured, and based on the measured runout, the angular position of the magnetic poles can be more accurately calculated. For example, the measured runout can be used to correct for variations or errors in the angular position of the magnetic poles. The measured runout can also be applied as a calibration factor to the data collected by the magnetic field sensors. The correction based on the determined runout can result in a more accurate measurement of the angular position of the first platform relative to the second platform.

[0031] In particular, runout can be determined based on measuring a phase shift detected by the magnetic field sensor relative to a sequence of nominal reference angles. As previously described, the angular position of the magnetic poles can be determined from measurements collected from the magnetic field sensor. In particular, the measured magnetic field can help determine the position of the magnetic poles on the magnet ring. The position of the magnetic poles on the magnet ring can be compared to the nominal position of the magnetic poles based on the corresponding nominal boundary to determine the angular difference of the actual magnetic pole positioning from the nominal magnetic pole positioning.

[0032] The angular difference of the magnetic pole position, which corresponds to the measured phase shift, can then be plotted to determine the runout. On a graph, the runout can resemble a sinusoidal curve. In particular, the sinusoidal curve can be a fixed periodic harmonic of the rotational frequency of the brushless DC motor. To more easily identify the sinusoidal variation, the DC component can be removed from the signal obtained by the magnetic field sensor. Once the AC component is plotted, the signal can take on a more sinusoidal shape. The amplitude of the sinusoidal curve can correspond to the amount of runout.

[0033] To remove the sinusoidal runout error from the plotted data, the data can be transformed by a Fourier transform. By removing the sinusoidal curve, the amount of runout that the brushless DC motor is experiencing can be removed from the signal detected by the magnetic field sensor. Removing the runout can improve the accuracy of determining the angular position of the first platform relative to the second platform. Additionally or alternatively, the runout determination can be used as a calibration factor when processing the data collected from the magnetic field sensor.

[0034] II. Example Rotary Joint

[0035] Figure 1 is a simplified block diagram of a device 100 that includes a rotary joint. As shown, the device 100 includes a first platform 110 and a second platform 130. The first platform 110 can include or can be coupled to a rotor or other movable component. For example, the platform 110 can be configured to rotate relative to the platform 130 and about an axis of rotation (e.g., a rotor axis) of the platform 110. Thus, the platform 110 can be configured as a rotating platform in a rotary joint configuration. As shown, the platform 110 includes a sensor 112, a controller 114, a communication interface 116, a power source interface 118, and one or more magnets 120.

[0036] In some examples, the platform 110 can include any solid material suitable to support and / or mount various components of the platform 110. For example, the platform 110 can include a printed circuit board (PCB) that mounts the communication interface 116 and / or other components of the platform 110. In such cases, the PCB can also include circuitry (not shown) to electrically couple one or more of the components of the platform 110 (e.g., the sensor 112, the controller 114, the communication interface 116, the power interface 118, etc.) to one another. In such cases, the PCB can be positioned such that the mounted components are along a side of the platform 110 that faces or is opposite a corresponding side of the platform 130. For example, with such an arrangement, the platforms 110 and 130 can be kept within a given distance relative to one another in response to rotation of the platform 110 relative to the platform 130.

[0037] The sensor 112 can include any combination of sensors mounted to the platform 110. A non-exhaustive list of example sensors can include directional sensors (e.g., IMUs, gyroscopes, accelerometers, etc.), remote sensing devices (e.g., radar, lidar, etc.), sound sensors (e.g., microphones), and other examples.

[0038] The controller 114 can be configured to operate one or more components of the first platform 110. To do so, the controller 114 can include any combination of general purpose processors, special purpose processors, data stores, logic circuits, and / or any other circuitry configured to operate one or more components of the device 100. In one implementation, the controller 114 includes one or more processors that execute instructions stored in a data store to operate the sensor 112, the interface 116, etc. In another implementation, the controller 114 instead or additionally includes wiring to perform one or more functions and processes described herein for operating one or more components of the device 100. In one example, the controller 114 can be configured to receive sensor data collected by the sensor 112 and provide a modulated electrical signal to the communication interface 116 indicative of the sensor data. For example, the sensor data can be indicative of a measured orientation, a scan of a surrounding environment, a detected sound, and / or any other sensor output of the sensor 112.

[0039] The communication interface 116 can include any combination of wireless or wired communication components (e.g., transmitters, receivers, antennas, light sources, light detectors, etc.) configured to send and / or receive data and / or instructions between the platforms 110 and 130. In one example, where the communication interface 116 is an optical communication interface, the interface 116 can include one or more light sources arranged to emit modulated light signals 102 for reception by a light detector included in the platform 130. For example, the signals 102 can be indicative of sensor data collected by the sensor 112. Further, in this example, the interface 116 can include a light detector to receive modulated light signals 104 emitted from the platform 130. For example, the signals 104 can be indicative of instructions for operating the sensor 112 and / or any other components coupled to the platform 110. In this case, the controller 114 can operate the sensor 112 based on the received instructions detected via the interface 116.

[0040] The power interface 118 can include one or more components configured for wireless (or wired) transmission of power between the platforms 110 and 130. By way of example, the interface 118 can include transformer coil(s) (not shown) arranged to receive magnetic flux extending through the transformer coils to induce a current for powering one or more components of the platform 110 (e.g., the sensor 112, the controller 114, the communication interface 116, etc.). For example, the transformer coils can be arranged about a central region of the platform 110 opposite a corresponding transformer coil included in the platform 130. Further, for example, the device 100 can also include a magnetic core (not shown) extending through the transformer coils in the interface 118 (and / or the transformer coil included in the platform 130) to direct the magnetic flux through the respective transformer coils, thereby improving the efficiency of power transmission between the two platforms. Other configurations are also possible.

[0041] The magnet(s) 120 can be formed of a ferromagnetic material such as iron, a ferromagnetic compound, a ferrite, etc., and / or any other material that is magnetized to produce a first platform magnetic field of the platform 110. For example, the magnet(s) 120 can be a neodymium-iron-boron (NdFeB) magnet. In another example, the magnet(s) 120 can not include iron in its composition, thus can be, for example, an aluminum-nickel-cobalt (AlNiCo) magnet, among other possibilities.

[0042] In one implementation, the magnets 120 can be implemented as a plurality of magnets in a substantially circular arrangement about the axis of rotation of the platform 110. For example, the magnets 120 can be arranged along a circle concentric with the axis of rotation to produce a combined magnetic field extending toward and / or through the platform 130. Further, for example, adjacent ones of the magnets 120 can be magnetized in alternating directions such that a pole of a given magnet along a surface of the given magnet facing the platform 130 is opposite a pole of an adjacent magnet along a similar surface. For example, with this arrangement, a magnetic field can extend from the surface of a given magnet toward the platform 130 and then toward the surface of an adjacent magnet. Further, another magnetic field can extend from the surface of the given magnet toward the platform 130 and then toward another adjacent magnet.

[0043] In another implementation, the magnets 120 can be implemented as a single annular magnet concentric with the axis of rotation of the first platform. In this implementation, the annular magnet can be magnetized to have a magnetization pattern similar to that of the plurality of magnets described above. For example, the annular magnet can be implemented as a printed magnet having a plurality of annular sectors (e.g., regions of the annular magnet between respective radial axes thereof). In this example, adjacent annular sectors of the annular magnet can be magnetized in alternating directions to define a plurality of alternating poles facing the platform 130.

[0044] In a further implementation, the magnets 120 can be implemented as a plurality of electromagnets in a substantially circular arrangement about the axis of rotation of the platform 110. In this implementation, the electromagnets can be magnetized (e.g., driven with a current having a particular direction) to have a magnetization pattern similar to that of the plurality of magnets described above. For example, adjacent electromagnets in the substantially circular arrangement can be magnetized in alternating directions to define a plurality of alternating poles facing the platform 130.

[0045] The second platform 130 can be configured as a stator platform in a rotary joint configuration. For example, the axis of rotation of the platform 110 can extend through the platform 130 such that the platform 110 rotates relative to the platform 130 while remaining within a given distance from the platform 130. As shown, the platform 130 includes a controller 134, a communication interface 136, a power interface 138, a conductive structure 140, circuitry 150, and a magnetic field sensor 190. To this end, the platform 130 can be formed from any combination of solid materials suitable to support various components mounted or otherwise coupled to the platform 130. In some examples, the platform 130 can include a circuit board of one or more components of the mounting apparatus 100 (e.g., the interfaces 136, 138, the sensor 190, etc.).

[0046] For example, like controller 114, controller 134 can have various physical implementations (e.g., a processor, a logic circuit, an analog circuit, a data store, etc.). Also, for example, like controller 114, communication interface 116, and signal 102, respectively, controller 134 can operate communication interface 136 to transmit a signal 104 indicative of a transmission of data or instructions. For example, controller 134 can operate interface 136 (e.g., a transceiver, an antenna, a light source, etc.) to provide a modulated wireless signal indicative of instructions for operating sensor 112 and / or any other component of platform 110. Also, for example, controller 134 can receive a modulated electrical signal from interface 136 indicative of a modulated signal 102 transmitted from platform 110.

[0047] Communication interface 136 can be implemented similarly to interface 116 to facilitate communication between platforms 110 and 130 via signals 102 and 104.

[0048] Power interface 138 can be configured similarly to power interface 118, and thus can operate in conjunction with power interface 118 to facilitate power transmission between platforms 110 and 130. By way of example, interface 138 can include a transformer coil (not shown), and controller 134 can be configured to cause a current to flow through the transformer coil. The current can then generate a magnetic flux that extends through a corresponding transformer coil (not shown) of power interface 118 to induce a current through the corresponding transformer coil. Thus, the induced current can power one or more components of platform 110.

[0049] Electrically conductive structure 140 can include portions of an electrically conductive material (e.g., copper, other metals, etc.) that are electrically coupled together to define an electrically conductive path that extends about an axis of rotation of platform 110 to overlap the first platform magnetic field generated by magnet(s) 120. By way of example, electrically conductive structure 140 can include a first plurality of electrically conductive structures in a first coplanar arrangement along a circle concentric with the axis of rotation of platform 110. Also, in this example, electrically conductive structure 140 can further include a second plurality of electrically conductive structures in a second coplanar arrangement to overlap the first plurality of electrically conductive structures parallel to the first plurality of electrically conductive structures. For example, in a circuit board implementation, the first plurality of electrically conductive structures can be disposed or patterned along a single layer of the circuit board, and the second plurality of electrically conductive structures can be disposed or patterned along another layer of the circuit board.

[0050] Continuing the above example, the device 100 can also include a plurality of electrical contacts (not shown), such as, for example, conductive material extending through a drill (e.g., via) between two layers of the circuit board. The electrical contacts can couple the first plurality of conductive structures to the second plurality of conductive structures to define one or more electrically conductive coils that extend about the axis of rotation to overlap the circular arrangement of the magnet(s) 120 of the first stage. The electrical circuit 150 (and / or the controller 134) can then cause one or more currents to flow through the one or more coils to generate a second stage magnetic field that extends within the one or more coils. The first stage magnetic field can then interact with the second stage magnetic field to provide a force or torque acting on the stage 110. The induced force can then cause the stage 110 to rotate about its axis of rotation. Moreover, in some cases, the electrical circuit 150 (and / or the controller 134) can modulate the second stage magnetic field by adjusting the current(s) flowing through the coil(s). By doing so, for example, the device 100 can control the direction or rate of rotation of the stage 110 about the axis of rotation.

[0051] Accordingly, the electrical circuit 150 can include any combination of wiring, conductive material, capacitors, resistors, amplifiers, filters, comparators, voltage regulators, controllers, and / or any other circuitry arranged to provide and modulate the current(s) flowing through the conductive structures 140. For example, the electrical circuit 150 can be configured to adjust the current(s) to modify the second stage magnetic field to achieve certain rotational characteristics (e.g., direction, speed, etc.) of the rotating stage 110.

[0052] The magnetic field sensor 190 can be configured to measure one or more characteristics (e.g., direction, angle, magnitude, flux density, etc.) of the first stage magnetic field associated with the magnet(s) 120. For example, the sensor 190 can include one or more magnetometers arranged to overlap the magnet(s) 120 and / or the first stage magnetic field. A non-exhaustive list of example sensors includes proton magnetometers, Overhauser effect sensors, cesium vapor sensors, potassium vapor sensors, rotating coil sensors, Hall effect sensors, magnetoresistive device sensors, fluxgate magnetometers, superconducting quantum interference device (SQUID) sensors, microelectromechanical system (MEMS) sensors, and spin-exchange relaxation free (SERF) atomic sensors, among other examples. In one implementation, the sensor 190 can include a three-dimensional (3D) Hall effect sensor that outputs an indication of the angle (and / or magnitude) of the first stage magnetic field at the location of the sensor 190 according to an orthogonal coordinate system representation (e.g., x-y-z axis components) or other vector field representation. In another implementation, the sensor 190 can include a binary Hall effect sensor that outputs a binary indication of the flux transition between magnetic poles. The transition between magnetic poles can hereafter be referred to as a hall tick.

[0053] Accordingly, the device 100 can use the output(s) from the sensor 190 as a basis for determining the orientation or position of the platform 110 about the axis of rotation. For example, the sensor 190 can be positioned to overlap a portion of the first platform magnetic field that extends between two adjacent magnets of the magnet(s) 120. As the first platform 110 rotates, the angle of this portion can change at the location of the sensor 190, and thus the circuit 150 (and / or the controller 134) can sample the output from the sensor 190 to infer the position of the sensor 190 relative to the two adjacent magnets.

[0054] Accordingly, with this arrangement, the device 100 can use the magnet(s) 120 as components (e.g., a magnetic encoder) for both actuating the platform 110 and measuring the orientation of the platform 110. This arrangement can provide an actuator and magnetic encoder with reduced cost and with a more compact design.

[0055] In some implementations, the device 100 can include fewer or more components than those shown. In one example, the device 100 can be implemented without the sensor 190 and / or any of the other components shown. In another example, the platforms 110 and / or 130 can include additional or alternative sensors (e.g., microphones, etc.), computing subsystems, and / or any other components. Additionally, it is noted that the various functional blocks shown can be arranged or combined differently than shown. For example, some of the components included in the platform 110 can instead be included in the platform 130 or implemented as a separate component of the device 100.

[0056] Figure 2 A side view of a device 200 including a rotary joint is shown. As shown, the device 200 includes a rotor platform 210 and a stator platform 230 that can be respectively similar to the platforms 110 and 130. In the example shown, a side 210a of the platform 210 is positioned at a given distance 208 from a side 230a of the platform 230. The platform 210 can be configured as a rotor platform that is rotatable about an axis of rotation 206. Further, the platform 230 can be configured as a stator platform that is held within the distance 208 from the platform 210 in response to rotation of the platform 210 about the axis of rotation 206 on a shaft 232. In some examples, the side 210a can correspond to a planar mounting surface (e.g., an outer layer of a circuit board) of the platform 210. Similarly, for example, the side 230a can correspond to a planar mounting surface of the platform 230.

[0057] Example embodiments can include an electric machine, such as a brushless DC electric machine. A magnet ring can be mounted to a first platform of the electric machine, and the magnet ring can include four or more magnetized poles. The electric machine can also include a plurality of magnetic field sensors connected to a second platform. The second platform can be configured to rotate about an axis relative to the first platform, and the plurality of magnetic field sensors can be configured to output signals used to produce a runout-corrected fingerprint associated with the electric machine. As the second platform rotates, the magnetic field sensors can detect a displacement at the axis caused by runout. The runout can cause a distance between the magnets and the magnetic field sensors to vary as the platform rotates. This displacement can manifest as an electrical phase shift in the signals collected by the magnetic field sensors.

[0058] In an example embodiment, the plurality of magnetic field sensors can be Hall effect sensors. The Hall effect sensors can collect data used to correct for runout and encoder error. The runout-corrected fingerprint can be produced by determining a phase difference between each Hall tick and an expected nominal position of each Hall tick. In an example embodiment, there can be a nominal position at which the magnetic field sensors should detect a Hall tick. However, the magnetic field sensors can measure an actual position of the Hall tick that can be different. This is the phase difference. The magnitude of the phase difference can be indicative of the amount of runout.

[0059] III. Example magnet ring with jittered poles

[0060] Figure 3 A magnet ring 300 with jittered poles is shown. Specifically, Figure 3 A top view of the magnet ring 300 is shown, which can be disposed, for example, on the side 230a of the platform 230. The magnet ring 300 can alternatively be referred to as a ring magnet, a magnetic ring, or simply a ring. In this example, the magnet ring 300 includes eight poles 302, 304, 306, 308, 310, 312, 314, and 316 (i.e., poles 302-316). The poles 302, 306, 310, and 314 are magnetized such that their respective north poles (“N”) face out of the page (i.e., pointing up from the platform 230 toward the platform 210). On the other hand, the poles 304, 308, 312, and 316 are magnetized such that their respective south poles (“S”) face out of the page (i.e., pointing down from the platform 230). Although the magnet ring 300 includes eight poles in this example, it will be understood that the number of poles can range, for example, from four poles to several hundred or several thousand poles, depending on the size of the magnet ring 300. The poles 302-316 can be defined by discrete magnets, by annular sectors of a ring magnet, or by electromagnets.

[0061] The boundaries between adjacent ones of the poles 302-316 (e.g., pole 302 and pole 304) are dithered. That is, the boundaries are shifted relative to where they would be if each of the poles had equal dimensions. In other words, each of the poles 302-316 has a slightly different dimension, resulting in a non-uniform spacing (i.e., asymmetric distribution) of the pole boundaries around the magnet ring 300.

[0062] In Figure 3 The lines 320, 322, 324, 326, 328, 330, 332, and 334 (i.e., lines 320-334) illustrate where the pole boundaries would fall if each of the poles 302-316 had equal dimensions. That is, the lines 320-334 illustrate a uniform spacing (i.e., symmetric distribution) of the pole boundaries along the magnet ring 300. The boundaries defined by the lines 320-334 can be referred to as nominal boundaries. However, in the magnet ring 300, each of the actual boundaries between adjacent ones of the poles 302-316 is shifted relative to a corresponding one of the nominal boundaries 320-334 by a respective amount, defining a characteristic dithering pattern of the pole boundaries. For example, the pole 304 begins before the line 322 and ends after the line 324, whereas the pole 304 would begin at the line 322 and end at the line 324 if it were not for such dithering.

[0063] The respective pattern of shifts in the transitions or boundaries between the poles 302-316 can be used to determine a rotational position of the magnet ring 300 relative to another structure that is rotating relative to the magnet ring 300. In particular, during operation, the transitions between adjacent poles can be measured by a magnetic field sensor. The measured transitions can then be compared to the known transition pattern of the magnet ring 300 to identify its rotational position, as described in more detail below. For example, a position of the platform 230 (to which the magnet ring 300 can be coupled) relative to the platform 210 can be determined.

[0064] IV. Example sensor positioning for magnetic ring fingerprinting

[0065] As discussed above, a single magnetic field sensor can be used to detect a magnetic field pattern of the magnet ring 300 as it rotates. This magnetic field pattern can be compared to a characteristic field pattern to determine a rotational position of the magnet ring 300. Such a comparison can involve computing a correlation between the measured magnetic field pattern and the characteristic shift pattern. In one implementation, such a computation can be performed in steps of 1, resulting in a comparison of each detected shift value to each known shift value reflected in the characteristic shift pattern.

[0066] Additionally, in some embodiments, a system or device utilizing a magnet ring 300 can employ multiple magnetic field sensors to determine the position of the magnet ring 300. Notably, additional magnetic field sensors can be spaced around the circumference of the magnet ring 300, and thus can detect more pole transitions per a given time window or for a given angular displacement of the magnet ring 300 than a single magnetic field sensor.

[0067] Figure 4 An example arrangement of magnetic field sensors 400, 402, and 404 (i.e., sensors 400-404) around the magnet ring 300 centered on axis 232 is shown. Sensors 400-404 can be connected to side 210a of platform 210 such that they move relative to the magnet ring 300 (which is connected to side 230a of platform 230), and thus detect characteristic changes in the magnetic field across poles 302-316.

[0068] In one embodiment, sensor 400 can be disposed at 0 degrees, sensor 402 can be disposed at 100 degrees, and sensor 404 can be disposed at 220 degrees. That is, sensor 402 can be 100 degrees apart from sensor 400, sensor 404 can be 120 degrees apart from sensor 402, and sensor 404 can be 140 degrees apart from sensor 400. Thus, by rotating the magnetic ring 140 degrees, sensors 400-404 can collectively detect every transition thereon.

[0069] In some embodiments, sensors 400-404 can be spaced around the magnet ring 300 in a symmetrical fashion (e.g., 120 degrees apart from one another). In this case, a composite signature pattern can also be used to determine the position of the magnet ring 300 relative to sensors 400-404. However, the pattern produced by each of sensors 400-404 will repeat periodically every 120 degrees. For example, when the magnet ring 300 is rotated 120 degrees, sensor 402 will produce a first output pattern. When the magnet ring 300 is rotated another 120 degrees counterclockwise, sensor 400 will produce a second output pattern that is approximately identical to the first output pattern (except for any noise).

[0070] V. Example operations for determining runout

[0071] As discussed above, example embodiments can include methods for determining a runout factor of a rotating device. Specifically, runout can affect the data collected by a magnetic field sensor and cause errors in determining the angular position of a first platform. Runout can be represented as a sinusoidal linear error over one revolution. However, by measuring the linear error and separating that error from the signal detected by the magnetic field sensor, the runout error can be removed from the data.

[0072] Example embodiments can disclose tracking a phase difference between a measured position and an expected nominal position of each magnetic pole to determine runout. An increase or decrease in the magnet spacing compared to the nominal spacing can cause a change in the phase angle, which can be indicative of runout. Figure 5A and Figure 5B Runout is shown and how it corresponds to a phase difference detected by a magnetic field sensor. The figures can be related to at least one of devices 100 or 200. In the figures, platform 230 is centered on axis 232, but axis 232 is not at the common rotational axis 206 of the device. As platform 210 rotates, the magnetic field sensor can detect a displacement at axis 206 caused by runout. Runout can cause the distance between the magnets on platform 210 and the magnetic field sensor 400 to vary as the platform rotates. This displacement can manifest as an electrical phase shift in the signal collected by the magnetic field sensor.

[0073] In Figure 5A , when the magnetic field sensor 400 is closer to the magnetic ring 300, there can be a positive angle error. The positive angle error can be seen as an increase in speed at the sensor due to the sensor moving closer to the magnetic ring 300. However, in Figure 5B , when the magnetic field sensor 400 is further from the magnetic ring 300, there can be a negative angle error. The negative angle error can indicate a significant decrease in speed as the sensor is further from the magnetic ring.

[0074] Figure 6 A flowchart 600 of operations related to determining runout error is shown. These operations can be used with any of devices 100 or 200 or magnetic ring 300. These operations can be performed by, for example, controller 114, controller 134, or circuitry configured to perform these operations.

[0075] Block 602 can involve generating a first magnetic field that interacts with a second magnetic field generated by four or more magnetic poles of a magnetic ring mounted to a first platform such that the first platform rotates relative to a second platform about a rotational axis.

[0076] Block 604 can involve receiving, from a magnetic field sensor connected to the second platform, data indicative of a characteristic of the second magnetic field, wherein each respective boundary between adjacent ones of the four or more magnetic poles is shifted relative to a corresponding nominal boundary defined by a substantially uniform spacing of boundaries of the four or more magnetic poles about the magnetic ring.

[0077] Block 606 can involve determining a magnetic field pattern based on the data received from the magnetic field sensor. In some embodiments, the magnetic field pattern can alternatively be referred to as a measured magnetic field pattern.

[0078] Block 608 can involve determining, based on the magnetic field pattern, an angular position of the four or more magnetic poles of the magnet ring relative to the second platform. The angular position of the magnetic poles of the magnetic ring can be defined by using the magnetic field pattern to determine the position of the magnetic poles on the magnetic ring.

[0079] Block 610 can involve determining an angular difference between the angular position of the four or more magnetic poles of the magnet ring relative to the second platform and a nominal angular position defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnetic ring. In particular, the angular difference can be the difference between the measured position of the magnetic poles and the expected nominal position of the magnetic poles.

[0080] Block 612 can involve determining a runout error based on a magnitude of the angular difference. The magnitude can be defined by an amount of migration of the shaft 232 supporting both platforms away from the common axis 206 while rotating.

[0081] In some embodiments, determining the magnetic field pattern can be based on data produced by the magnetic field sensor while the first platform is rotated relative to the second platform. In an example embodiment, the first platform can be rotated at a constant speed during at least a portion of a full rotation.

[0082] In some embodiments, the data received from the magnetic field sensor can include transitions between adjacent magnetic poles of the four or more magnetic poles. For example, the magnetic field sensor can detect an edge of a magnetic pole. In particular, the magnetic field sensor can detect when the flux is zero.

[0083] In some embodiments, the angular positions can be determined with timestamps. An example embodiment can include receiving, from the magnetic field sensor, timestamps when the magnetic field sensor detects the four or more magnetic poles of the magnetic ring, and converting each timestamp to a corresponding angle using a constant speed assumption. The timestamps can form an array that indicates each time the magnetic field sensor detects a transition between magnetic poles of the magnetic ring. Each corresponding timestamp can be converted to determine an angular position of a magnetic pole of the magnetic ring. In particular, by knowing the time at which each magnetic pole is detected and by assuming a constant speed, the angular position of the magnetic pole of the magnet ring on the first platform can be determined. The result can include an array of angular positions of the magnetic poles.

[0084] An example embodiment can also include using the array of measured angular positions of the magnetic poles of the magnetic ring, and comparing it to an array of expected nominal angular positions of the magnetic poles of the magnetic ring to determine an array of angular differences between the two. The angular differences can also be considered as an array of offsets between the measured positions and the nominal positions.

[0085] In an example embodiment, the angle difference can also include a DC component and an AC component. Data collected by the magnetic field sensor during operation can include the overage between the magnetic poles of the magnetic ring and can include both an AC component and a DC component. As previously discussed, the signal from the magnetic field sensor can be used to determine runout. Thus, because the angle difference can be based on the signal obtained by the magnetic field sensor, the angle difference can also include an AC component and a DC component.

[0086] In an example embodiment, the DC component can be removed from the angle difference to determine an AC signal, which can then be plotted. Removing the DC component can improve the ability to determine runout. As previously discussed, the angle difference can include an array including the angle difference for the position of each respective magnetic pole of the magnetic ring. In an example embodiment, a de-bias function can be used to calculate an average DC bias for each element in the angle difference array. Although a de-bias function can be used to calculate the average DC bias, it will be understood that many other methods can be used to calculate the bias. Each element in the angle difference array can be returned with the DC component removed. The AC component of the angle difference in the position of the magnetic poles of the magnet ring can then be plotted.

[0087] An example embodiment can also include plotting the angle difference and fitting a graph of the angle difference to a sinusoidal curve. The angle difference can be indicative of a phase shift of the measured magnetic pole position relative to an expected nominal position. In an example embodiment, the operations can include plotting a signal indicative of the phase shift obtained by the magnetic field sensor. The runout error can be based on the amplitude of the sinusoidal curve. To fit the graph of the angle difference to a sinusoidal curve, the method can include using a non-linear least squares fit of a sinusoidal function with a fixed period. Alternatively, a fast Fourier transform can be used to fit the graph of the angle difference to the best matching sinusoidal wave. It will be understood that other methods can also be used to fit the graph to a sinusoidal curve.

[0088] Figure 7A A graph of the angle difference in each of the various positions detected by the magnetic field sensor of the transition between the magnetic poles of the magnetic ring is shown. The horizontal axis of the graph indicates the degrees of the angle difference, and the horizontal axis represents each transition between the magnetic poles in the magnetic ring. Thus, the graph can show the shift between the measured angular position of the magnetic poles of the magnetic ring and the expected nominal angular position. However, the graph also shows how the runout error appears as a sinusoidal curve in the signal. As previously discussed, the runout can cause an erroneous detection of the position of the magnetic poles on the magnet ring. Figure 7A The deviation of the angle difference is shown to increase as the runout increases. Specifically, the angle difference oscillates with the sinusoidal runout error. This is caused by the at least one platform being laterally shifted, thus causing a significant change in the detected distance between the magnetic poles on the magnetic ring.

[0089] An example embodiment can also include determining a runout calibration factor based on the runout and applying the calibration factor to data received by the magnetic field sensor. The runout calibration factor can be based on an amplitude of a sinusoidal bias in the angle difference signal. Further, applying the calibration factor can include subtracting a sinusoidal component from the plotted angle difference to determine a more correct position of the magnetic poles on the magnet ring. For example, the sinusoidal component can be removed by subtracting an array containing values at each angular position of the magnetic poles of the magnet ring of a sinusoidal curve from an array containing measured angular positions of the magnetic poles of the magnet ring of equal length. The array containing values at each angular position of the magnetic poles of the magnet ring of a sinusoidal curve can be produced using parameters gathered from fitting a plot of the angle difference as a sinusoidal curve. It will be understood that a variety of ways for subtracting the sinusoidal component are possible. Figure 7B A plot of the angle difference at each of the various positions of the transitions between the magnetic poles of the magnetic ring detected by the magnetic field sensor once the sinusoidal runout error has been removed and the results calibrated is shown. The resulting plot does not include the sinusoidal variation in the signal. Thus, the angle difference appears much more accurate.

[0090] In an example embodiment, the method can include determining a phase shift based on the magnetic field pattern and a nominal magnetic field pattern. The nominal magnetic field pattern can be defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnetic ring. The phase shift can be a change in phase between the measured magnetic field pattern and the nominal magnetic field pattern. An amplitude of the phase difference can be indicative of an amount of runout.

[0091] An example embodiment can also include a non-transitory computer readable storage medium to run at least some of the operations previously described. In particular, the non-transitory computer readable medium can have stored thereon instructions that, when executed by a computing device, cause the computing device to perform the operations.

[0092] The operations can involve providing instructions to produce a first magnetic field by causing a current to flow through a conductive path. The first magnetic field can interact with a second magnetic field produced by four or more magnetic poles of a magnet ring mounted to a first platform such that the first platform rotates relative to a second platform about an axis of rotation. The conductive path can be included in the second platform.

[0093] The operations can involve receiving data from a magnetic field sensor connected to the second platform indicative of a characteristic of the second magnetic field. Each respective boundary between adjacent ones of the four or more magnetic poles can be shifted relative to a corresponding nominal boundary defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnet ring.

[0094] The operations can also involve determining a magnetic field pattern based on the data received from the magnetic field sensor. In some embodiments, the magnetic field pattern can be alternatively referred to as a measured magnetic field pattern. Based on the magnetic field pattern, the operations can include determining an angular position of the four or more magnetic poles of the magnet ring relative to the first platform. The angular position of the magnetic poles of the magnetic ring can be defined by using the magnetic field pattern to determine the position of the magnetic poles on the magnetic ring.

[0095] The operations can also involve determining a phase difference. The phase difference can be an angular difference between the angular position of the four or more magnetic poles of the magnet ring relative to the first platform and a nominal angular position defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnet ring. In particular, the angular difference can be defined as a difference between the measured position of the magnetic poles and an expected nominal position of the magnetic poles.

[0096] The operations can involve plotting the angular difference. The angular difference can be indicative of a phase shift of the measured magnetic pole position relative to the expected nominal position. In an example embodiment, the operations can include plotting a signal indicative of the phase shift obtained by the magnetic field sensor. Finally, the operations can involve determining a runout error based on a magnitude of the plotted angular difference. The magnitude can be defined by an amount of migration of the shaft supporting the two platforms away from the common axis while rotating.

[0097] VI. Additional example operations

[0098] As discussed above, a single magnetic field sensor can be used to detect a magnetic field pattern of a magnet ring while the magnet ring is rotating. Additional magnetic ring sensors can also be added to more accurately detect the magnetic field pattern of the magnetic ring. This can improve the estimated position of the magnetic poles on the magnetic ring. Furthermore, determining a runout error can ultimately improve determining individual positions of the magnetic poles on the magnet ring.

[0099] Figure 8 A flowchart 800 showing operations related to mitigating post-calibration errors in a brushless DC motor is shown. These operations can be used with any of the devices 100 or 200 or the magnet ring 300. These operations can be performed by, for example, the controller 114, the controller 134, or circuitry configured to perform these operations.

[0100] Block 802 can involve generating a first magnetic field that interacts with a second magnetic field generated by four or more magnetic poles of a magnet ring mounted to a first platform such that the first platform rotates relative to a second platform about an axis of rotation.

[0101] Block 804 can involve receiving, from a magnetic field sensor connected to the second platform, data indicative of a characteristic of the second magnetic field. Each respective boundary between adjacent ones of the four or more magnetic poles can be shifted relative to a corresponding nominal boundary defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnet ring.

[0102] Block 806 can involve determining, based on the data received from the magnetic field sensor, a signal defined by the angular position of the four or more magnetic poles of the magnet ring relative to the second platform. In some embodiments, this signal can alternatively be referred to as a measured signal.

[0103] Block 808 can involve determining a difference signal between the signal defined by the angular position of the four or more magnetic poles of the magnet ring relative to the second platform and a nominal signal defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnetic ring. The difference signal can be considered to indicate a shift between the measured signal indicative of the position of the magnetic poles on the magnetic ring and the expected nominal signal indicative of the position of the magnetic poles on the magnetic ring.

[0104] Block 810 can involve removing a sinusoidal component from the difference signal to determine a phase fingerprint signal. In an example embodiment, the difference signal can include a sinusoidal error component due to runout in the brushless DC motor. When experiencing runout, the distance between the magnetic field sensor and the magnetic poles on the magnet ring fluctuates. The runout can be represented by a sinusoidal component as the signal collected by the magnetic field sensor. By removing the sinusoidal component, a more accurate difference between the measured signal and the nominal signal can be determined. This difference can be expressed in terms of a phase shift. The phase shift can be used to determine the phase fingerprint signal.

[0105] Block 812 can involve determining, based on the phase fingerprint signal, a position of the magnetic poles of the magnet ring on the first platform, where the position includes a spacing between each boundary between adjacent ones of the four or more magnetic poles. Because the phase fingerprint signal indicates a difference between the measured magnetic pole position and the nominal magnetic pole position on the magnet ring, the specific position of the magnetic poles on the magnetic ring on the first platform can be more accurately determined.

[0106] An example embodiment can also include determining, based on the position of the magnetic poles of the magnet ring, a magnetic ring fingerprint, and determining, based on the fingerprint, a spacing error of each boundary between adjacent magnetic poles. Once a particular magnetic ring fingerprint is determined, it can be used to determine whether the spacing of the magnetic ring exceeds a threshold amount from the nominal spacing. If the threshold is exceeded, there can be a spacing error.

[0107] An example embodiment can also include the data received from the magnetic field sensor including a transition between adjacent ones of the four or more magnetic poles. As the first platform rotates, the magnetic field sensor can detect when each magnetic pole on the magnetic ring passes the magnetic field sensor. The magnetic field sensor can also detect the transition based on detecting a flux with a zero value.

[0108] An example embodiment can include a plurality of magnetic field sensors, wherein the data indicative of the characteristic of the second magnetic field is received from the plurality of magnetic field sensors. Each of the previously described operations can then be completed for each of the individual magnetic field sensors. For example, the position of the poles of the magnet ring on the first platform can be calculated with each magnetic field sensor.

[0109] An example embodiment can include collecting, with the plurality of magnetic field sensors, magnetic field data resulting from the rotation of the second platform relative to the first platform. The method can further include generating, based on the collected magnetic field data, an array of the angular positions of the four or more poles of the magnet ring relative to the first platform as detected by each of the individual magnetic field sensors. By separating each element in the array, the operations can be performed on each element. An example embodiment can include separating the array of angular positions based on the individual magnetic field sensors. For each magnetic field sensor, the position of the poles of the magnet ring on the first platform can be determined.

[0110] An example embodiment can include, for each of the individual magnetic field sensors, comparing the angular positions of the four or more poles of the magnet ring relative to the first platform to each other. An example embodiment can further include, based on the comparison, determining an error in at least one of the magnetic field sensors. Each magnetic field sensor should collect data indicative of the positions of the poles on the magnet ring that are within a threshold distance of each other. However, if after comparing the data, the position within the threshold distance detected by one of the sensors is different than the position determined by the other sensors, then there can be an error in the sensor.

[0111] VII. CONCLUSION

[0112] The present disclosure is not limited to the particular embodiments described in this application, which are intended as illustrations only. Many modifications will occur to one skilled in the art upon the reading and understanding of the present disclosure. For example, it will be apparent that certain aspects of the disclosure can be performed in a different order than the order described herein. As will be apparent to those skilled in the art, certain features of the disclosure which are, individually, not essential to the practice of the disclosure can be relinquished. In addition to the variations described herein, other equivalents to the features of the disclosure will be apparent to those skilled in the art in view of the preceding descriptions and drawings. Such modifications and variations are intended to fall within the scope of the appended claims. It is the intent of the applicant(s) that all such variations and modifications be considered as falling within the true spirit and scope of the disclosure.

[0113] The above detailed description describes various features and functions of the disclosed systems, devices, and methods with reference to the accompanying drawings. In the drawings, like reference numerals generally refer to like parts throughout the various figures and views. The example embodiments described herein are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are implicitly contemplated herein.

[0114] The blocks representing information processing can correspond to circuits configurable to perform a particular logical function in connection with the methods or techniques described herein. Alternatively or additionally, the blocks representing information processing can correspond to modules, segments or portions of program code (including related data). The program code can include one or more instructions that are executable by a processor to implement a particular logical function or action in the methods or techniques. The program code or related data can be stored on any type of computer readable medium (such as a storage device including a magnetic or optical hard disk drive) or other storage medium.

[0115] Computer readable media can also include non-transitory computer readable media, such as computer readable media that store data for short periods of time, like register memory, processor cache and Random Access Memory (RAM). Computer readable media can also include non-transitory computer readable media that store program code, or data, for longer periods of time, like secondary or persistent long term storage, like read only memory (ROM), Optical Disc or magnetic hard disk drive, Compact Disc Read Only Memory (CD-ROM). Computer readable media can also be any other volatile or non-volatile storage systems. A computer readable medium can be considered a computer readable storage medium, or a tangible storage device, for example.

[0116] Furthermore, the blocks denoting one or more information transmissions can correspond to information transmissions between software or hardware modules in the same physical device. However, other information transmissions can be between software modules or hardware modules in different physical devices.

[0117] The particular arrangement of elements shown in the drawings is not to be understood as limiting. It is to be understood that other embodiments can include more or less of each element shown in the given drawing. Furthermore, some elements shown may

[0118] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the appended claims.

Claims

1. A method comprising: generating a first magnetic field that interacts with a second magnetic field generated by four or more magnetic poles of a magnet ring mounted to a first platform such that the first platform rotates relative to a second platform about an axis of rotation; receiving, from a magnetic field sensor connected to the second platform, data indicative of a characteristic of the second magnetic field, wherein the second magnetic field is generated by the four or more magnetic poles of the magnet ring; determining, based on the data received from the magnetic field sensor, a measured signal; determining a nominal signal, wherein the nominal signal is indicative of a characteristic field pattern; determining a difference signal between the measured signal and the nominal signal, wherein the difference signal comprises a phase shift between the measured signal and the nominal signal; and determining a runout error based on a magnitude of the difference signal; determining a runout calibration factor based on the runout error; and applying the runout calibration factor to the data received by the magnetic field sensor, wherein applying the runout calibration factor comprises subtracting a runout array comprising values of the difference signal from a measured array comprising values of the measured signal.

2. The method of claim 1, further comprising determining the magnetic field pattern based on data generated by the magnetic field sensor while the first platform rotates relative to the second platform.

3. The method of claim 2, wherein the data received from the magnetic field sensor comprises a transition between adjacent ones of the four or more magnetic poles.

4. The method of claim 3, wherein the magnetic field pattern further comprises an array of time stamps for each respective transition between adjacent ones of the magnetic poles.

5. The method of claim 1, further comprising determining an angular position of the four or more magnetic poles of the magnet ring relative to the second platform, comprising: receiving, from the magnetic field sensor, a time stamp when the magnetic field sensor detects the four or more magnetic poles of the magnet ring; and converting each time stamp to a respective angle using a constant velocity assumption. the angle difference further comprises a DC component and an AC component.

7. The method of claim 6, further comprising:

6. The method of claim 5, further comprising determining an angular difference between an angular position of the four or more magnetic poles of the magnet ring relative to the second stage and a nominal angular position, and wherein, removing the DC component from the angle difference to determine an AC signal; and plotting the AC signal.

8. The method of claim 1, further comprising plotting the difference signal and fitting a plot of the difference signal to a sinusoidal curve, and wherein the runout error is based on a magnitude of the sinusoidal curve.

9. The method of claim 1, wherein the phase shift comprises a change in phase of the magnetic field pattern from a nominal magnetic field pattern.

10. A method of mitigating post-calibration errors in a brushless DC motor, comprising: generating a first magnetic field that interacts with a second magnetic field generated by four or more magnetic poles of a magnet ring mounted to a first platform such that the first platform rotates relative to a second platform about an axis of rotation; receiving, from a magnetic field sensor connected to the second platform, data indicative of a characteristic of the second magnetic field, wherein the second magnetic field is generated by the four or more magnetic poles of the magnet ring; determining, based on the data received from the magnetic field sensor, a measured signal; determining a nominal signal, wherein the nominal signal is indicative of a characteristic field pattern; ​ ​ ​ determining a difference signal between the measured signal and the nominal signal, wherein the difference signal comprises a phase shift between the measured signal and the nominal signal; removing a sinusoidal component from the difference signal to determine a phase fingerprint signal; determining, based on the phase fingerprint signal, a position of the magnetic poles of the magnet ring on the first platform, wherein the position comprises a spacing between a plurality of respective boundaries between adjacent ones of the four or more magnetic poles; and applying the difference signal to data received from the magnetic field sensor, wherein applying the difference signal comprises subtracting the difference signal from the measured signal.

11. The method of claim 10, further comprising: determining a magnetic ring fingerprint based on the position of the magnetic poles of the magnet ring; and determining a spacing error in the boundaries of the adjacent magnetic poles based on the magnetic ring fingerprint.

12. The method of claim 10, wherein the data received from the magnetic field sensor comprises a transition between adjacent ones of the four or more magnetic poles.

13. The method of claim 11, further comprising a plurality of magnetic field sensors, wherein the data indicative of the features of the second magnetic field is received from the plurality of magnetic field sensors.

14. The method of claim 13, wherein the position of the magnetic poles of the magnet ring on the first platform is computed with each magnetic field sensor.

15. The method of claim 14, further comprising: collecting, with the plurality of magnetic field sensors, magnetic field data resulting from rotation of the second platform relative to the first platform; and generating, based on the collected magnetic field data, an array of angular positions of the four or more magnetic poles of the magnet ring relative to the first platform as detected by each of the respective magnetic field sensors.

16. The method of claim 15, further comprising: separating, based on the respective magnetic field sensors, the array of angular positions; and determining, for each magnetic field sensor, the position of the magnetic poles of the magnet ring on the first platform.

17. The method of claim 16, further comprising: comparing, for each of the respective magnetic field sensors, the angular positions of the four or more magnetic poles of the magnet ring relative to the first platform to one another; and determining, based on the comparison, an error in at least one of the magnetic field sensors.

18. An electric machine, comprising: a magnet ring mounted on a first platform, wherein the magnet ring comprises four or more magnetized poles; a plurality of magnetic field sensors connected to a second platform, wherein the second platform is configured to rotate about an axis relative to the first platform, and wherein the plurality of magnetic field sensors are configured to output a signal for generating a run-out corrected fingerprint associated with the electric machine, wherein generating the run-out corrected fingerprint associated with the electric machine comprises: generating a first magnetic field that interacts with a second magnetic field generated by the four or more magnetic poles of the magnet ring mounted to the first platform such that the first platform rotates about the axis of rotation relative to the second platform; receiving, from the plurality of magnetic field sensors connected to the second platform, data indicative of features of the second magnetic field, wherein each respective boundary between adjacent ones of the four or more magnetic poles is offset relative to a corresponding nominal boundary defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles about the magnet ring; determining, based on the data received from the magnetic field sensors, a measured signal defined by the angular position of the four or more magnetic poles of the magnetic ring relative to the second platform; determining a difference signal between the measured signal and a nominal signal defined by a substantially uniform spacing of the boundaries of the four or more magnetic poles around the magnet ring, wherein the difference signal includes a phase shift between the measured signal and the nominal signal; removing a sinusoidal component from the difference signal to determine a phase fingerprint signal; determining, based on the phase fingerprint signal, a run-out corrected fingerprint associated with the electric machine; and applying the difference signal to the data received from the magnetic field sensors, wherein applying the difference signal includes subtracting the difference signal from the measured signal.

19. The electric machine of claim 18, wherein the plurality of magnetic field sensors are Hall effect sensors, and the run-out corrected fingerprint is generated by determining a phase difference between each Hall tick and an expected nominal position of each Hall tick.

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