Position sensor having harmonic distortion compensation

Methods and apparatus for determining a mechanical angle of a target from sine and cosine signals generated by inductive sensing elements by applying harmonic compensation on the sine and cosine signals using possible mechanical angles and analyzing results of the applied harmonic compensation. One of the mechanical angles can be selected based on the results of the applied harmonic compensation. In embodiments, a cost function can be used to select the mechanical angle.

BACKGROUND

As is known in the art, inductive sensors, such as rotary sensors, can be provided as an angle sensor for detecting the position or speed of a rotating target. In particular, inductive rotary sensors can be used to detect the position of a gear or another moving element in a mechanical system. They are frequently used in automated control applications, such as automated control applications in automobiles or industrial equipment, for example. As is also known harmonic components may decrease sensor accuracy.

SUMMARY

Example embodiments of the disclosure provide methods and apparatus for detecting unambiguous mechanical angle position of multi-pole angle sensors with analog sine/cosine outputs which contain information of the single pole-pair angle (electrical angle). Embodiments of the disclosure are applicable to multi-pole angle sensors in general in which enhanced angle sensing is desirable. In some embodiments, sensor embodiments comprise inductive eddy current angle sensors. Signal processing of sensed signals can be performed in the sensor integrated circuit (IC) package, an IC interfaced to the sensor, remote circuit board, or the like, that receives the analog signals from the sensing elements.

In embodiments, harmonic content of the sine/cosine signals is known and has been stored, such as in memory. Where the harmonic content is known, a mechanical reference is determined by applying harmonic coefficients with mechanical angle guess(es) and performing a Fourier Transform, such as a discrete Fourier transform (DFT). The mechanical angle that provides minimum harmonic content in the DFT results can be selected.

In some multi-pole inductive position sensors, the electrical angle includes errors that can be related to a specific pole and, therefore, to the mechanical absolute position. Having the mechanical angle information or knowing on which pole is the sensor, the host system can apply further corrections to have a more accurate angle information. In many electric motor applications with multi poles, there may be some mechanical tolerance or imperfection in the motor design related to a specific pole (for example due to bended teeth/runout/manufacturing tolerances, etc.), making the angle calculation less accurate. Knowing the absolute angle allows for additional compensation and enhanced accuracy.

In embodiments, an IC or host calculates electrical angle θel using sine and cosine analog signals with the following formula: θel=a tan 2(Sine/Cosine) and applies harmonic compensation on the sine and cosine signals N times using the N possible mechanical angle (θm) position values spaced by 360 electrical degree: θm=θel/N+k*360/N where k can vary from 0 to N−1. A set of N pairs of sine and cosine compensated signals is obtained. On each of the N compensated signals a DFT can be performed using estimated mechanical angle as a reference for sampling at uniform intervals. At the end of a full mechanical revolution (equal to N electrical periods) without direction change, the DFT providing a minimum cost, for example, of higher order harmonics, e.g., except the desired first electrical harmonic (Nth mechanical harmonic), identifies the proper mechanical angle for correct harmonic compensation.

In one aspect, a method comprises: determining a mechanical angle of a target from sine and cosine signals generated by sensing elements; applying harmonic compensation on the sine and cosine signals for possible mechanical angles; analyzing results of the applied harmonic compensation; and selecting one of the mechanical angles for harmonic compensation of the sine and cosine signals based on the results of the applied harmonic compensation.

A method can further include one or more of the following features: the sensing elements comprise inductive sensing elements, the sensing elements comprise magnetic sensing elements, the sine and cosine signals are generated by a transmit coil and at least two receiving coils, analyzing the results includes using a cost function, selecting one of the mechanical angles comprises selecting the mechanical angle with the lowest value from the cost function, applying the harmonic compensation on the sine and cosine signals includes performing a Fourier transform, the harmonic compensation for the mechanical angles is stored, determining the harmonic compensation information over at least one mechanical revolution of a target at constant speed and/or using an absolute angle reference, the sensing elements comprise part of a multi-pole angle sensor IC package, the sensor IC package comprises an inductive eddy current angle sensor, the possible mechanical angles are defined by

θ⁢m=θ⁢e⁢lN+k*3⁢6⁢0/N
where k can vary from 0 to N−1, θm refers to mechanical angle, θel refers to electrical angle, and N refers to a number of teeth on the target, and/or the results of the applied harmonic compensation include amplitudes of undesired harmonic components.

In another aspect, a system comprises: an integrated circuit (IC) package including circuitry to: receive sine and cosine signals from sensing elements; apply harmonic compensation on the sine and cosine signals for possible mechanical angles of a target; analyze results of the applied harmonic compensation; and select one of the mechanical angles for harmonic compensation of the sine and cosine signals based on the results of the applied harmonic compensation.

A system can further include the sensing elements comprise inductive sensing elements, the sensing elements comprise magnetic field sensing elements, the sine and cosine signals are generated by a transmit coil and at least two receiving coils, the results are analyzed using a cost function, one of the mechanical angles is selected based on a lowest value from the cost function, applying the harmonic compensation on the sine and cosine signals includes performing a Fourier transform, the harmonic compensation for the mechanical angles is stored, the harmonic compensation information is determined over at least one mechanical revolution of a target at constant speed and/or using an absolute angle reference, the sensing elements comprise part of a multi-pole angle sensor IC package, the sensor IC package comprises an inductive eddy current angle sensor, the possible mechanical angles are defined by

θ⁢m=θ⁢e⁢lN+k*3⁢6⁢0/N
where k can vary from 0 to N−1, θm refers to mechanical angle, θel refers to electrical angle, and N refers to a number of teeth on the target, the results of the applied harmonic compensation include amplitudes of undesired harmonic components, a sensor IC package containing the sensing elements, wherein the sensor IC package is coupled to the IC package, and/or the IC package comprises and engine control unit.

In a further aspect, a system comprises: means for receiving sine and cosine signals from sensing elements; and means for processing the sine and cosine signals including: applying harmonic compensation on the sine and cosine signals for possible mechanical angles of a target; analyzing results of the applied harmonic compensation; and selecting one of the mechanical angles for harmonic compensation of the sine and cosine signals based on the results of the applied harmonic compensation.

DETAILED DESCRIPTION

Example embodiments of the disclosure provide a sensor, such a magnetic field sensor or an inductive sensor having coils, such as a transmit coil and a receive coil(s), with mechanical angle detection using harmonic component information. A target having one or more teeth, e.g., N>=1, can be fixed to a rotatory shaft, for example. A signal injected by the transmit coil results in the receiving coil(s) sensing a signal at the carrier frequency of the signal transmitted by the transmit coil. A sinusoidal amplitude modulation of the received signal is dependent upon the angular position of the target. Harmonic information, which may be stored, can be used to remove distortion from higher order harmonic components to increase sensor accuracy.

FIG.1shows an example inductive sensor100for position sensing having mechanical angle detection in accordance with example embodiments of the disclosure. The sensor100includes a sensing element102having a transmitting coil104and at least first and second receiving coils106,108. As illustrated, the sensor100may also include an LC tank110that is configured to drive the transmitting coil104. In operation, the LC tank110may cause the transmitting coil104to transmit a direct magnetic field112that may induce a second magnetic field114(hereinafter “reflected magnetic field114”) in a target116. The receiving coils106and108may receive the reflected magnetic field114and output cosine Vc and sine Vs signals, respectively.

The sine and cosine signals Vc and Vs may be described below:
Vc=K1cos(θel)*sin(2πfrt)
VS=K2sin(θel)*sin(2πfrt)
where, K1is a coupling coefficient associated with the first receiving coil106, K2is a coupling coefficient for the second receiving coil108, θelis the electrical angle of the target116in the target's electrical period, fris the resonant frequency of the LC tank110, and t is time. It is understood that the carrier signal is contained in the sin(2πfrt) portion and the signal envelop containing the angular information is contained in K1cos(θel).

According to the present disclosure, the electrical angle of the target116indicates the angular position of the target in its electrical period. The coupling coefficient K1indicates the proportion of the flux of the reflected magnetic field114that is sensed by the first receiving coil106. And the coupling coefficient K2indicates the proportion of the magnetic flux of the reflected magnetic field114that is sensed by the second receiving coil108. In other words, the coupling coefficients may indicate the proportion of energy transmitted by the target116that is received by the first and second receiving coils106,108.

When N=1, the envelop of the received signal represents the sine and cosine information of the mechanical angle. When N>1, the envelop represents the sine and cosine of the electrical angle (θel). In one mechanical revolution of the target (360 degrees), there are N electrical rotations (N*360). The electrical angle can be defined as

θ⁢⁢el=atan⁢⁢2⁢(sincos).
The mechanical angle may be ambiguous and defined as

θ⁢m=θ⁢e⁢lN+k*3⁢6⁢0/N,
where k can vary. The electrical angle of the target116may be based on the mechanical angle of the target (with respect to the sensor100) and the number of lobes in each portion of the receiving coils106,108. According to the present disclosure, the mechanical angle of the target116indicates the orientation of the target116relative to the sensor100and/or the sensing element102.

It is understood that a variety of sensing element types can be used to generate sine and cosine signals for which it may be desirable to identify an ambiguous mechanical angle. Example sensors generating sine and cosine signals for which mechanical angle identification may be performed in accordance with embodiments of the disclosure include U.S. Pat. Nos. 7,714,570, 8,786,279, 9,739,847, and 10,585,147, all of which are incorporated herein by reference.

FIG.2is a schematic diagram of an example implementation of the sensing element102ofFIG.1. As illustrated, in the example ofFIG.1, the sensing element102includes a receiving coil that is used to measure the speed (and/or angular displacement) of a target116. The receiving coil may include a first coil portion106and a second coil portion108. The first coil portion106and the second coil portion108may include 1 lobe each. The target116may have a main portion130, a tooth132, and a valley134. As illustrated, the tooth132and the valley134may each have a respective arc length that is equal to 180 degrees.

FIG.3shows an example sensing element102′ having a target where N=4. In some implementations, the number of teeth in the target of the system may be equal to the number of lobes in each coil portion of the receiving coils of the system. According to the example ofFIG.3, the target116′ of the sensing element has four (4) teeth, the first coil portion of the receiving coil106′ may have four (4) lobes and the second coil portion of the receiving coil108′ may have four (4) lobes. The sensing element102′ may be used to measure the rotational displacement and/or speed of the target116′.

FIG.4shows an example implementation of a sensing element, such as the sensing element102ofFIG.1. As can be seen, the transmit coil104, the first receiving coil106, and the second receiving coil108are provided in PCB layers in an example stack up. The target116is positioned a given distance from the sensor100.

As shown inFIG.5, undesirable harmonic frequencies can reduce accuracy of sensors. In general, signals from the receiving coils are not ideal sine and cosine waveforms for the electrical angle of the target. In addition to the desired first electrical harmonic, higher order harmonic components may be present. As can be seen, mechanical harmonic number can be plotted versus harmonic amplitude. The signal of interest for the mechanical harmonic is θ(el)=N*θ(m). Harmonic components at N+/−1, N+/−2, etc., are undesirable since they reduce the accuracy of the sensor by generating an error in the electrical angle information.

FIG.6Ashows an example received sine signal over mechanical angle with harmonic distortion and an example received cosine signal over mechanical angle with harmonic distortion. In the illustrated waveforms N=5.FIG.6Bshows electrical angle error over mechanical angle for the sine and cosine signals ofFIG.6A. The electrical angle error over mechanical angle provides a signature for the harmonic distortion. As described more fully below, the electrical angle error can be used to identify the mechanical angle.

In embodiments, undesired harmonic components that generate error in the angular position can be removed if the harmonic components of the sine and cosine signals, e.g., amplitude Aiand phase φiand the reference mechanical angle for the harmonic component phase are known. If these are known, the corrected sine and cosine signals can be obtained by subtracting out the undesired harmonic components. This can be expressed as:
SineCorrected=Sine−ΣiAisin(i*θm+φm)
CosineCorrected=Cosine−ΣiAisin(i*θm+φm)

Obtaining harmonic information can be performed in a variety of ways. For example, harmonic components can be determined by using a Discrete Fourier Transform (DFT) for target rotating at a constant speed over at least one mechanical cycle, e.g., 360 degrees. Also, harmonic components can be determined using an absolute reference angle during calibration, for example. It is understood that any practical technique can be used to obtain harmonic component information to meet the needs of a particular application. Once obtained, the harmonic component information can be stored and used to remove harmonic-based error, as described more fully below.

FIG.7shows example processing to perform harmonic processing in accordance with example embodiments of the disclosure. In the illustrative embodiment, N=5. In step700, sine and cosine signals are acquired, which may be similar to the signals shown inFIG.6A.FIG.7Ashows example harmonic amplitude and phase information for a series of mechanical harmonics. In embodiments, the signals ofFIG.6Aand harmonic information inFIG.7Aare used for calibration. The harmonic data can be stored to perform harmonic distortion compensation.FIG.7Bshows an estimated mechanical angle on the left side for each of k=0 to 4 and corrected sine and cosine signals for each value of k on the right side. As can be seen, k=3 is the value to select for finding the reference for mechanical angle reconstruction and harmonic compensation.FIG.7Cshows a sum of the harmonic amplitudes for k=0 to 4. As can be seen, k=3 has the lowest cost value.FIG.7Dshows electrical angle and reconstructed mechanical angle for starting period k=3.

In step702, the electrical angle θel is calculated from sine and cosine signals, such as from receiving coils. In embodiments, electrical angle θel is calculated as:

It is understood that the sine and cosine signals are raw signals that include harmonic distortion so that the electrical angle θel has error due to the harmonic components.

In step704, harmonic compensation is applied to the sine and cosine signal N times using N possible mechanical angles, which can be expressed as:

θ⁢m=θ⁢e⁢lN+k*3⁢6⁢0/N
where k can vary from 0 to N−1.

A set of N pairs of compensated sine and cosine signals are obtained. In step706, a DFT can be performed on the signals using estimated angle as a reference for sampling at uniform intervals. The output of the DFT is the harmonic content of the corrected signals in amplitude and phase.

In embodiments, at end of a full mechanical revolution (equal to N electrical periods) without direction change, in step708the DFT providing a minimum cost of all harmonic expect the first electrical harmonic (Nth mechanical harmonic) identifies the proper mechanical angle for correct harmonic compensation. The cost function can be defined as the sum by summing up harmonic component magnitudes (except fundamental):
Ck=HM1+HM2+HM3+ . . . +HN−1+HN+1+ . . . +H2N
where HMxis the amplitude of x mechanical harmonics, and calculated harmonics are summed except for the system desired harmonic (HN). When the mechanical angle used for compensation (number of k shifts of 360 electrical degree) corresponds to the same one as the one the stored harmonic content, the cost function has its minimum. Once the mechanical angle reference is known, the IC or host can use it memory or for other applications to apply the harmonic compensation on the signals with the stored harmonic information. The procedure can be applied in parallel or in series.

It is understood that any suitable cost function can be used to meet the needs of a particular application. For example, a root mean squared of harmonic amplitudes can be used.

In embodiments, a sensor system can include an interface IC to drives the sensor by providing the carrier signal to the transmitting (primary coil) and receives and conditions the signals from the receiving coils and transmit them to a host. The interface IC can calculate the electrical angle information to transmit it to the host. The host may include a microcontroller, an engine control unit (ECU), or the like, that receives the conditioned signals or the electrical angular information from the Interface IC. This information can be transmitted in analog or digital forms. The sensor and the interface IC may be configured to provide the host with accurate electrical angle information.

FIG.8is a diagram of an example of a system800, according to aspects of the disclosure. As illustrated, the system800may include an electric motor810, a target802, a sensor804, an interface circuit820, and an electronic control unit (ECU)830. The target802may be coupled to a rotor of the electric motor810(not shown), and it may rotate with the rotor. The sensor804may detect the rotation of the target802and output signals Vcand Vsto the interface circuit820after harmonic compensation, as described above. The interface circuit820may be coupled to the ECU830via lines832-838. Line832may be used by the ECU830to provide ground to the interface circuit820. Line834may be used by the ECU830to provide power to the interface circuit. Line836may be used by the interface circuit820to provide the signal Vcto the ECU830. And line838may be used by the interface circuit820to provide the signal Vsto the ECU830. Based on the signals Vcand Vs, the ECU830may determine the electric angle θelof the target300, in accordance with Equation 8 below.

The electrical angle θelof the target802may be used by the ECU830to determine the speed and/or mechanical angle of the target802. Based on the speed and/or mechanical angle of the target802, the ECU830may adjust the speed of (or stop) the electric motor810. It will be understood that the present disclosure is not limited to any specific method for using the speed and/or mechanical angle of the target802. Although in the example ofFIG.8the sensor804is used to control the speed of an electric motor, it will be understood that the present disclosure is not limited to any specific application of the sensor804. For example, the sensor804can be used to control shifting in automotive transmissions and/or any other suitable application. In this regard, although in the example ofFIG.8the interface circuit820is coupled to an ECU, it will be understood that alternative implementations are possible in which the interface circuit820is coupled to another type of electronic circuitry.

FIG.9shows an exemplary computer900that can perform at least part of the processing described herein. The computer900includes a processor902, a volatile memory904, a non-volatile memory906(e.g., hard disk), an output device907and a graphical user interface (GUI)908(e.g., a mouse, a keyboard, a display, for example). The non-volatile memory906stores computer instructions912, an operating system916and data918. In one example, the computer instructions912are executed by the processor902out of volatile memory904. In one embodiment, an article920comprises non-transitory computer-readable instructions.

Processing may also be implemented as a machine-readable storage medium, configured with a computer program, where upon execution, instructions in the computer program cause the computer to operate.

Processing may be performed by one or more programmable processors executing one or more computer programs to perform the functions of the system. All or part of the system may be implemented as, special purpose logic circuitry (e.g., an FPGA (field programmable gate array), a general purpose graphical processing units (GPGPU), and/or an ASIC (application-specific integrated circuit)).

Having described exemplary embodiments of the disclosure, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may also be used. The embodiments contained herein should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.