AND ROTATING AXIAL TARGET SURFACE

[0001] This relates generally to rotational sensing for angle, frequency and direction, such as used for sensing motor (generator) rotation.

BACKGROUND

[0002] Electric motors include a rotor that rotates within a stationary stator. Either the rotor or stator is formed with permanent magnets, and the other component is formed with current-carrying windings. For example, stepper motors typically use a magnetic rotor with stator windings.

[0003] In implementations where the rotor is formed of magnetic material, motor current drive to the stator windings generates a rotating magnetic field that completes one revolution in one cycle of the stator currents, with a rotor angular velocity that depends on the frequency of the current drive.

[0004] Motor drive systems can be designed for adjustable speed control, and bi-directional motor rotation. Motor control requires a system for sensing motor rotation information, such as rotational frequency, angle and direction. However, rotational sensing systems for stepper and other motor applications are susceptible to EMI (electromagnetic interference) from the stator magnetic field coupled into the sensing system.

SUMMARY

[0005] Described examples include methods and apparatus for rotational sensing with inductive sensor(s) and a rotating axial target surface, such as can be adapted for use in a motor applications (such as a positioner/stepper motor).

[0006] According to one example, a rotational sensing methodology is adaptable for use in sensing rotation of a rotor, and useable in a rotational sensing system that includes an axial target surface configured for axial rotation with the rotor, and that includes at least one conductive target segment, and that includes an inductive sensor mounted adjacent the axial target surface, including at least one inductive sense coil that is substantially parallel to and spaced from the axial target surface, such that rotor rotation causes the target segment to rotate laterally under the sense coil during each rotor rotation cycle.

[0007] The methodology includes driving excitation current to the sense coil to project a time -varying magnetic sensing field (B-field) toward the axial target surface, thereby inducing eddy currents in the target segment as it rotates under the sense coil. In response to the rotation of the at least one target segment relative to the at least one sense coil and its projected B-field, the inductive sensor generates a sensor response characterized by a sensor phase cycle, so: (a) the sensor phase cycle initiates at a phase_cycle_L _M iN in which the sense coil is aligned with the target segment to output a minimum sensor response L _MIN corresponding to maximum induced eddy current; (b) the sensor phase cycle transitions through a phase cycle LMAx in which the sense coil is misaligned with the target segment to output a maximum sensor response corresponding to minimum induced eddy current; and (c) the sensor phase cycle ends with the initiation of a next sensor phase cycle at phase_cycle_L _M iN; and (d) the number of sensor phase cycles in a rotor rotation cycle corresponds to the number of target segments.

[0008] The methodology further includes: (a) acquiring sensor response measurements corresponding to sensor response for the at least one sense coil in successive sensor phase cycles, including phase_cycle_L _M iN and phase_cycle_L _M Ax; and (b) converting the sensor response measurements to sensor response data representative of rotation information for the rotating axial target surface that correlates to the sensor response measurements. Sensor response data can correspond to at least one of rotational frequency and rotational angle

[0009] In various described examples, the axial target surface can include multiple target segments evenly spaced on the axial target surface, and the inductive sensor can include multiple sense coils, in number equal to or less than the number of target segments, and arranged relative to the multiple target segments, such that sensor phase cycles are synchronized, so that sensor responses are synchronized. The multiple sense coils and the multiple target segments are configured, such that the sensor response from the multi-coil inductive sensor throughout a rotor rotation cycle is a substantially sinusoidal sensor response signal that cycles between phase_cycle_L _M iN and phase_cycle_L _M Ax in a succession of sensor 360° phase cycles. The inductive sensor can include at least one sense coil pair with first and second sense coils wound with opposite polarity, such that the sensor response of the paired sense coils throughout a rotor rotation cycle is a substantially sinusoidal sensor response signal that cycles between phase_cycle_L _M iN and phase_cycle_LMAx as a succession of sensor 360° phase cycles. The inductive sensor can include at least one set of I and Q sense coils arranged relative to the at least one target segment, such that the respective sensor I and Q phase cycles are offset by an IQ phase offset, and such that: for rotation in one direction, the sensor I phase cycle lags the sensor Q phase cycle; and for rotation in the other direction, the sensor I phase cycle leads the sensor Q phase cycle, thereby enabling converting the I and Q sensor response measurements to sensor response data corresponding to rotation direction information for the rotating axial target surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 illustrates an example functional embodiment of a rotational sensing system adapted for use in an example motor application.

[0011] FIGS. 2A, 2B, 2C illustrate an example functional embodiment of a rotational sensing system, configured for reduced sensitivity to common mode EMI.

[0012] FIGS. 3A and 3B illustrate an example functional embodiment of a rotational sensing system, configured for directional sensing.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0013] The example embodiments illustrate various features and advantages of rotational sensing with inductive sensor(s) and rotating axial target surface.

[0014] In brief overview, a rotational sensing system is adaptable to sensing motor rotation based on eddy current sensing. An axial target surface is mounted to the motor rotor, and includes one or more conductive target segment(s). An inductive sensor is mounted adjacent the axial target surface, and includes one or more inductive sense coil(s), such that rotor rotation rotates the target segment(s) laterally under the sense coil(s). An inductance-to-digital conversion (IDC) unit drives sensor excitation current to project a magnetic sensing field (B-field) toward the rotating axial target surface. Sensor response is characterized by successive sensor phase cycles that cycle between: phase_cycle_L _M iN in which a sense coil is aligned with a target segment; and phase_cycle_L _M Ax in which the sense coil is misaligned. The number of sensor phase cycles in a rotor rotation cycle corresponds to the number of target segments. The IDC converts sensor response measurements from successive sensor phase cycles into rotational data/information. In example embodiments: (a) oppositely-wound paired sense coils reduce susceptibility to common mode EMI; and I and Q paired sense coils are phase shifted (IQ phase offset) to enable sensing rotational direction.

[0015] FIG. 1 illustrates an example functional embodiment of a rotational sensing system adapted for use in an example motor application (such as a positioner/stepper motor), and including an axial target surface 20 and inductive sensor 30.

[0016] A motor 10 is functionally illustrated with a housing 11, stators 13 and a rotor 15 configured for rotor rotation about a rotor shaft. For the example stepper motor application, the rotor is constructed with permanent magnets, and the stators include stator windings, which are driven by the motor drive system to generate the stator magnetic field drives motor/rotor rotation.

[0017] A rotational sensing system is incorporated into motor 10, and adapted to sense rotation of rotor 15. Example embodiments of rotational sensing are functionally illustrated in: (a) FIGS. 2 A and 2B, including paired sense coils that are oppositely wound to reduce susceptibility to common mode EMI; and (b) FIG. 3A, including I and Q paired sense coils that are phase shifted to enable sensing rotational direction.

[0018] The rotational sensing system includes an axial target surface 20 incorporated for rotation with rotor 15, and an inductive sensor 30 (non-rotating) mounted parallel to and spaced from rotating axial target surface 20. Axial target surface 20 can include one or more conductive target segments. Sensor 30 can include one or more sense coils, parallel to and spaced from axial target surface 20. In various embodiments, the target segments can be evenly spaced around the axial target surface, and multiple sense coils can be: (a) paired (to reduce susceptibility to common mode EMI), as in the example embodiments of FIGS. 2A, 2B, 2C, 3A and 3B; and/or (b) arranged symmetrically relative to the target segments to increase readout/measurement magnitude, as in the example embodiment of FIGS. 2A, 2B and 2C; and/or (c) arranged with an IQ offset to enable sensing rotational direction, as in the example embodiment in FIGS. 3 A and 3B.

[0019] Axial target surface 20 is incorporated into motor 10 for axial rotation with rotor 15. As illustrated, axial target surface 20 is constructed as an axial carrier (disc) mounted to rotor 15. Alternative implementations include forming axial target surface 20 (including one or more conductive targets) on a corresponding surface of rotor 15, and using existing conductive elements of a surface of rotor 15 (such that the rotor surface provides the axial target surface). The target segment(s) can be formed onto axial target surface 20 in various suitable ways, such as separate conductive elements or by conductive patterning.

[0020] Referring to FIG. 1, and the example implementations in FIGS. 2A, 2B and 3 A, a rotational sensing system includes an axial target surface 20 (with multiple target segments), an inductive sensor 30 (with multiple sense coils), and an inductance-to-digital converter (IDC) 50.

[0021] Axial target surface 20 is configured for axial rotation with rotor 15, and includes one or more conductive target segment(s). Inductive sensor 30 is mounted within motor 10, adjacent axial target surface 20, and includes one or more inductive sense coil(s) that is/are substantially parallel to and spaced from the axial target surface. Rotor rotation causes the target segment(s) to rotate laterally under the sense coil(s) during each rotor rotation cycle.

[0022] In the example embodiments of FIGS. 2 A, 2B and 3 A, the axial target surface is configured with multiple, evenly spaced target segments 21-23, and inductive sensor 30 is configured with multiple sense coils, which are: (a) in FIGS. 2A and 2B, two oppositely-wound paired sense coils 31 A, 3 IB and 33A, 33B; and (b) in FIG. 3A, oppositely-wound and phase-shifted I and Q paired sense coils 30I A, 30I B and 30Q A, 30Q B. Rotor rotation is clockwise, and each target segment rotates laterally under each sense coil during each rotor rotation cycle.

[0023] IDC 50 is coupled to the inductive sense coil(s). In FIGS. 2A and 2B, IDC 50 is configured with a single channel 30 series coupled to coils 31 A, 3 IB and 33A, 33B. In FIG. 3A, IDC 50 is configured with dual I/Q channels 301, 30Q coupled respectively to the I and Q paired sense coils 30I A, 30I B and 30Q A, 30Q B, each oppositely wound arranged with an IQ offset (illustrated as an example quarter phase cycle offset).

[0024] IDC 50 represents sensor electronics configured for sensor excitation, and sensor response acquisition (measurement/readout) and conversion to sensor response data representative of rotational information (such as sensor readout data samples). IDC 50 drives AC excitation current to the sense coil(s) to project a time -varying magnetic sensing field (B-field) toward the rotating axial target surface. IDC 50 acquires sensor response measurements corresponding to sensor response for the sense coil(s) in successive sensor phase cycles. IDC 50 converts the analog sensor response measurement/readout to sensor response data representative of rotation information for the rotating axial target surface (which correlates to the sensor response measurement/readout). IDC implementations can require sensor response measurements with a minimum total inductance that cannot be provided by the sense coil(s), in which case the sense coil(s) can be coupled to the inductive transducer through an additional inductance (such as an external inductor). [0025] The sensor response data/information can be used for processing/generating rotational information, such as by a rotation processing unit (e.g., an MCU). Examples of such rotational information are rotational frequency, angle and/or direction.

[0026] As an example implementation, a rotational sensing system can be implemented based on resonant inductive sensing in which inductive sensor 30 and IDC 50 are configured for resonant sensing. Inductive sensor 30 can be configured with a sensor resonator circuit including one or more series-coupled sense coil inductor(s), with a series/parallel resonator capacitor. The sense coil inductor(s) and a series/parallel resonator capacitor form a sensor resonator tank circuit (which can be configured with a separate series/external inductor to supply a minimum effective inductance readout to IDC 50). Losses in the sensor resonator (LC tank circuit) can be characterized by a resistance Rs in series with the sense coil inductor(s), and referred to as sensor losses.

[0027] For sensor excitation, IDC 50 can be configured to drive the sensor resonator to maintain a resonance state of sustained (steady-state) oscillation. A driven resonator sense coil inductor projects a sensing B-field, which induces eddy currents in a target segment that rotates through the projected B-field. For implementations with multiple series coupled sense coil inductors, IDC 50 drives the multi-coil sensor resonator, so that each sense coil inductor generates a projected sensing B-field to the rotating axial target surface.

[0028] For sensor response acquisition, IDC 50 can be configured to acquire measurement/readout corresponding to sensor (resonator) response to the rotating target segment(s), as reflected in changes in the resonance state of the sensor resonator. For example, sensor resonator response can be based on either measuring eddy current losses manifested as a change in sensor resonator losses, or measuring a change in sense coil inductance (due to a change in eddy current back emf), manifested as a change in resonator frequency. In the case of eddy current losses, the sensor resonator losses can be characterized by series resistance Rs, or an equivalent resonator parallel impedance Rp (Rp = (l/Rs)*(L/C)), with changes in total sensor resonator impedance (1/Rp), which is a function of both inductance and resistance, measured as a change in the negative impedance (-1/Rp) required to counterbalance sensor resonator impedance, and maintain sensor resonance (sustained oscillation). In the case of sensor resonator inductance, changes in back emf caused by the induced eddy currents effectively changes sensor (coil) inductance, which is manifested as a corresponding change in resonator oscillation frequency required to maintain sensor resonance (sustained oscillation).

[0029] Independent of the method of eddy current sensing (based on resonant inductive sensing, or otherwise), a resonant sensing system, including sensor 30 and IDC 50, can be configured for sensor response readout based on either eddy current losses in the conductive target segments reflected as a change in sensor losses, or eddy current-induced back emf that changes effective sensor inductance. Design considerations include required sensitivity and tolerance for temperature effect. For example, eddy current sensing based on sensor eddy current losses is more sensitive, but sensor inductance is less susceptible to temperature effects.

[0030] In this example, sensor inductance is a convenient reference for sensor response (such as L _MIN and L _M A _X as used in FIGS. 2C and 3B). Unless the context clearly indicates that inductance is intended, reference to sensor response based on inductance, and in particular L _MIN and L _M A _X , is a reference to sensor response in general, including changes in sensor inductance based on back emf caused by induced eddy currents, but also including changes in sensor losses resulting from induced eddy current losses, and also including changes in total sensor impedance based on changes in sensor resistance and sensor inductance. In this example, sensor response is independent of how it is characterized, manifested or measured.

[0031] Referring to FIGS. 2A and 2B, and the example sensor response waveform in FIG. 2C, in response to the rotation of a target segment relative to the sense coil(s) and projected B-field(s), the sensor response is characterized by a sensor phase cycle. In the example functional embodiments of FIGS. 2A and 2B, rotor rotation is clockwise, so that: (a) for example, target segment 21 rotates clockwise under sense coil 31 A; (b) in FIG. 2A, target segment 21 is aligned with sense coil 31 A (and its projected B-field); and (c) in FIG. 2B, they are misaligned.

[0032] A sensor response phase cycle initiates at phase_cycle_L _M iN in which a sense coil is aligned with a target segment (FIG. 2A, 31 A, 21) to output a minimum sensor response L _MIN

(FIG. 2C, 35), corresponding to maximum induced eddy current (maximum eddy current losses). The sensor phase cycle transitions through a phase_cycle_L _M Ax where the sense coil (FIG. 2B, 31 A) is misaligned with the target segment (FIG. 2B, 21) to output a maximum sensor response ^ _M A (FIG. 2C, 35), corresponding to minimum induced eddy current (minimum eddy current losses). The sensor phase cycle ends with the initiation of a next sensor phase cycle at phase_cycle_L _M iN- The number of sensor phase cycles in a rotor rotation cycle corresponds to the number of target segments.

[0033] IDC 50 is configured to acquire sensor response measurements corresponding to sensor response for the sense coil(s) in successive sensor phase cycles, each including transitioning between phase_cycle_L _M iN and phase cycle LMAx- IDC 50 converts the sensor response measurements from successive sensor phase cycles to sensor response data corresponding to rotation information for the rotating axial target surface that correlates to the sensor response measurements.

[0034] The example implementations illustrated in FIGS. 2 A and 2B (with an example sensor response waveform in FIG. 2C) and FIG. 3A (with an example sensor response waveform in FIG. 3B) illustrate rotational sensing using multiple target segments and multiple sense coils. The multiple target segments 21-23 are evenly spaced on the axial target surface. The number of sense coils is preferably equal to the number of target segments. The multiple sense coils are arranged relative to the multiple target segments, such that sensor phase cycles are synchronized, so that sensor responses are synchronized.

[0035] Specifically, the multiple target segments 21-23 are evenly spaced on the axial target surface, and arranged relative to the sense coil(s), such that the sensor response from the inductive sensor for the sense coil(s) throughout a rotor rotation cycle is a substantially sinusoidal sensor response signal that cycles between phase_cycle_L _M iN and phase_cycle_L _M Ax in a succession of sensor 360° phase cycles, as illustrated in the example sensor response waveforms in FIG. 2C (35) and FIG. 3B (351, 35Q).

[0036] FIGS. 2A, 2B and 3 A are functional illustrations not drawn to scale. The number, dimensions, placement, and shapes of the target segments and sense coils will depend on the dimensions of the axial target surface (rotor), and represent design trade-offs (including resolution, sensitivity and EMI). For example, while rotation sensing in this example requires only a single target and a single sense coil (such as in applications where only rotation counting is required), multiple targets can be used for: (a) increasing rotational/angular resolution (i.e., resolving the phase angle of the rotor within a phase cycle determined by the number/arrangement of target segments); and (b) for evenly spaced target segments, enabling a sinusoidal-type sensor response. Multiple sense coils can be used for increasing sensitivity (readout magnitude) through additive sensor responses from the multiple sense coils with synchronized sensor response phase cycles. Increasing the number of target segments increases resolution, but requires decreasing sense coil size, which decreases sense coil inductance, and which can impact manufacturability. Increasing the number of sense coils decreases (through averaging) the impact of system mechanical noise, such as due to vibration and mechanical tolerances (such as affecting coil-to-surface distance). Thus, advantageous configurations can include a maximum number of target segments and corresponding number of sense coils, although EMI consideration can require configurations with an even number of sense coils (oppositely wound), and so that this number of target segments can be limited to the number of sense coils plus one.

[0037] FIGS. 2A, 2B, 2C illustrate an example functional embodiment of a rotational sensing system, configured for reduced sensitivity to common mode EMI, including paired sense coils 31 A, 3 IB and 33A, 33B, wound with opposite polarity. FIG. 2A illustrates paired sense coils 31A, 31B aligned with target segments 21, 22, and paired sense coils 33A, 33B aligned with target segments 23, 24. FIG. 2B illustrates, after rotor rotation (clockwise), that paired sense coils 31A, 31B are misaligned with target segments 21, 22, and that paired sense coils 33A, 33B are misaligned with target segments 23, 24. FIG. 2C illustrates an example waveform 35 cycling between L _MIN and L _M A _X in successive sinusoidal sensor phase cycles.

[0038] Specifically, the rotational sensing system is configured with: (a) one or more paired sense coils, wound with opposite polarity; and (b) at least one target segment pair, arranged on the axial target surface, such that the sensor phase cycles for the paired sense coils are synchronized relative to the target segment pair.

[0039] In the example implementation of FIGS. 2A and 2B, multiple target segments 21-23 are evenly spaced on the axial target surface incorporated with rotor 15. Inductive sensor 30 includes two paired sense coils 31 A, 3 IB and 33A, 33B (oppositely wound). The paired sense coils 31 A, 3 IB and 33A, 33B are arranged relative to target segments 21-23, such that the sensor phase cycles for the paired sense coils are synchronized (and additive for increased readout magnitude).

[0040] Referring to FIG. 2A, rotor 15 has rotated, such that: (a) paired sense coils 31 A, 3 IB are aligned with target segments 21, 22; and (b) paired sense coils 33 A, 33B are aligned with target segments 23 and 24. Referring to FIG. 2B, rotor 15 has rotated (clockwise), such that: (a) paired sense coils 31A, 31B are now misaligned with target segments 21, 22; and (b) paired sense coils 33A, 33B are now misaligned with target segments 23 and 24.

[0041] Referring to the example sensor response waveform in FIG. 2C, the sensor response of the paired sense coils 31 A, 3 IB and 33A, 33B throughout a rotor rotation cycle is a substantially sinusoidal sensor response signal 35 that cycles between phase_cycle_L _M iN and phase_cycle_LMAx as a succession of sensor 360° phase cycles.

[0042] FIGS. 3 A and 3B illustrate an example functional embodiment of a rotational sensing system, configured for directional sensing (and for reduced sensitivity to common mode EMI). FIG. 3 A illustrates separate I and Q paired sense coils 30I A, 30I B and 30Q A, 30Q B (oppositely wound), arranged with: (a) an IQ phase offset of one quarter of the sensor I and Q 360° phase cycle; (b) I sense coils 30I_A, 30I_B respectively aligned with target segments 21, 23; and (c) the Q sense coils 30Q A, 30Q B respectively offset by the IQ offset relative to target segments 22, 24. FIG. 3B illustrates example waveforms 351 and 35Q with a one quarter IQ phase offset, cycling between LMIN and LMAX in successive sinusoidal sensor phase cycles, for clockwise rotation with 351 lagging 35Q, and for counter-clockwise rotation with 351 leading 35Q.

[0043] Specifically, the rotational sensing system is configured with one or more sets of I and Q paired sense coils (oppositely wound) arranged relative to the target segment(s), such that the respective sensor I and Q phase cycles are offset by an IQ phase offset, and such that: (a) for rotation in one direction, the sensor I phase cycle lags the sensor Q phase cycle; and (b) for rotation in the other direction, the sensor I phase cycle leads the sensor Q phase cycle.

[0044] In the example implementation of FIG. 3 A, multiple target segments 21-23 are evenly spaced on the axial target surface of rotor 15. Separate I and Q paired sense coils 30I A, 30I B and 30Q A, 30Q B (oppositely wound) are arranged with an IQ phase offset of one quarter (90°) of the sensor I and Q 360° phase cycle. At the illustrated point in the rotation cycle of rotor 15, the I sense coils 30I_A, 30I_B are respectively aligned with target segments 21 and 23, and the Q sense coils 30Q A, 30Q B are respectively offset relative to target segments 22 and 24 by the IQ phase offset of one quarter (90°) of the sensor I and Q 360° phase cycle.

[0045] Referring to the example sensor response waveforms in FIG. 3B, for the I and Q paired sense coils 30I A, 30I B and 30Q A, 30Q B (oppositely wound), the I and Q sensor responses throughout a rotor rotation cycle are respective substantially sinusoidal I and Q sensor response signals 351 and 35Q, each cycling between phase_cycle_L _M iN and phase_cycle_LMAx in a succession of sensor I and Q 360° phase cycles, offset in phase by the IQ phase offset of one quarter (90°) of the sensor I and Q 360° phase cycle. For clockwise rotation, sensor response sinusoid 351 lags sensor response sinusoid 35Q. For counter-clockwise rotation, sensor response sinusoid 351 leads sensor response sinusoid 35Q.

[0046] IDC 50 converts the I and Q sensor response signals to sensor response data corresponding to rotation direction information for the rotating axial target surface.

[0047] The foregoing describes various aspects and technical features of a rotational sensing system suitable for use in sensing rotation of a rotor. The rotational sensing system includes an axial target surface incorporated into the rotor, an inductive sensor configured for sensing rotor rotation, and an IDC unit configured to capture sensor response measurements/readings representative of rotor rotational information. The axial target surface is configured for axial rotation with the rotor, and includes at least one conductive target segment. The inductive sensor is mounted adjacent the axial target surface, including at least one inductive sense coil that is substantially parallel to and spaced from the axial target surface, such that rotor rotation causes the target segment to rotate laterally under the sense coil each rotor rotation cycle. The IDC unit is coupled to the at least one sense coil, and configured to drive excitation current to the sense coil to project a time -varying magnetic sensing field (B-field) toward the axial target surface, thereby inducing eddy currents in the target segment as it rotates under the sense coil. In response to the rotation of the at least one target segment relative to the at least one sense coil and its projected B-field, the inductive sensor generates a sensor response characterized by a sensor phase cycle, so that: (a) the sensor phase cycle initiates at a phase_cycle_L _M iN in which the sense coil is aligned with the target segment to output a minimum sensor response L _MIN corresponding to maximum induced eddy current; (b) the sensor phase cycle transitions through a phase_cycle_LMAx in which the sense coil is misaligned with the target segment to output a maximum sensor response corresponding to minimum induced eddy current; (c) the sensor phase cycle ends with the initiation of a next sensor phase cycle at phase_cycle_L _M iN; and (d) the number of sensor phase cycles in a rotor rotation cycle corresponds to the number of target segments. The IDC unit is further configured to: (a) acquire sensor response measurements corresponding to sensor response for the at least one sense coil in successive sensor phase cycles, including phase_cycle_L _M iN and phase cycle LMAx; and (b) convert the sensor response measurements to sensor response data representative of rotation information for the rotating axial target surface that correlates to the sensor response measurements. Rotational information can correspond to at least one of rotational frequency and rotational angle [0048] In various embodiments, the inductive sensor can include at least one sense coil pair with first and second sense coils wound with opposite polarity, and at least one target segment pair arranged on the axial target surface, such that the sensor phase cycles for the paired sense coils are synchronized relative to the target segment pair. The axial target surface can include multiple target segments evenly spaced on the axial target surface, such that the sensor response of the paired sense coils throughout a rotor rotation cycle is a substantially sinusoidal sensor response signal that cycles between phase_cycle_L _M iN and phase_cycle_L _M Ax as a succession of sensor 360° phase cycles.

[0049] In other embodiments, the inductive sensor can include at least one set of I and Q sense coils arranged relative to the at least one target segment, such that the respective sensor I and Q phase cycles are offset by an IQ phase offset, and such that: (a) for rotation in one direction, the sensor I phase cycle lags the sensor Q phase cycle; and (b) for rotation in the other direction, the sensor I phase cycle leads the sensor Q phase cycle. The IDC unit is further configured to convert I and Q sensor response measurements to sensor response data corresponding to rotation direction information for the rotating axial target surface. The axial target surface can include multiple target segments evenly spaced on the axial target surface, such that: (a) the I and Q sensor responses of the I and Q sense coils throughout a rotor rotation cycle are substantially sinusoidal I and Q sensor response signals; and (b) each cycle between phase_cycle_L _M iN and phase cycle LMAx, in a succession of sensor I and Q 360° phase cycles, respectively offset in phase by the IQ phase offset (such as substantially a quarter of the sensor I and Q 360° phase cycle).

[0050] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.