Patent Description:
Magnetostrictive sensors are a type of sensor that employs magnetic fields for measuring mechanical stresses, such as torque. As an example, a magnetostrictive sensor can generate a magnetic flux that permeates a rotating shaft and it can measure the magnetic flux as it interacts with the rotating shaft. The intensity of the measured magnetic flux can vary due to changes in stress experienced by the rotating shaft. Thus, magnetostrictive sensors can output stress signals representative of stress applied to a rotating shaft based upon magnetic flux measurements. In certain embodiments, torque can be calculated from stress and the geometry of the shaft.

While the magnetic flux measured by a magnetostrictive sensor can depend upon the stress applied to the rotating shaft, it can also depend upon a distance or gap separating the magnetostrictive sensor from the surface of the rotating shaft. As a result, stress signals acquired by a magnetostrictive sensor can also vary due to changes in this physical gap (e.g., due to vibrations), independently of the stress applied to the rotating shaft. For example, a non-ideal environment may result in vibrations of the rotating shaft and attendant changes in the gap. If gap-related changes in measured stress signals are not accounted for, the sensitivity and accuracy of stress measurements output by the magnetostrictive sensor can be reduced.

For this reason, it can be desirable to reduce the sensitivity of stress measurements acquired by the magnetostrictive sensor to the gap, referred to herein as gap compensation. As an example, a gap-dependent stress signal acquired by a magnetostrictive sensor can be combined with another gap-dependent signal to yield a gap-compensated stress signal. The gap-dependent stress signal and the gap-dependent signal can be combined in a suitable manner such that the gap-compensated stress signal possesses significantly reduced sensitivity to gap, as compared to the gap-dependent stress signal.

As an example, the gap-dependent signal can be acquired using a proximity sensor, such as an eddy current proximity probe. However, the magnetic properties of the target can vary about its circumference. Under this circumstance, the gap-dependent signal measured by a proximity sensor can change during rotation of the target, independently of change in the gap, referred to as electrical runout. Electrical runout can lead to introduction of error in the gap-dependent signal that repeats every revolution of the target. Thus, use of a gap-dependent signal containing error due to electrical runout for gap compensation can propagate this error to the gap-compensated stress signal. Accordingly, there is a need for systems and corresponding methods that provide relatively clean, gap-dependent signals exhibiting reduced sensitivity to electrical runout for use in gap compensation.

In one embodiment, a system is provided that includes a magnetostrictive sensor, a drive circuit, and a controller. The magnetostrictive sensor can include a drive coil configured to generate a magnetic flux in response to receipt of a current. The drive circuit can be in communication with the drive coil and configured to provide the current. The drive circuit can include a first sensing element and a second sensing element. The first sensing element can be in parallel with the drive coil and it can be configured to measure a first electrical property proportional to a voltage applied across the drive coil as a function of time while the generated magnetic flux interacts with at least a portion of a target. The first sensing element can also be configured to generate a first signal based upon the first electrical property measurement. The second sensing element can be configured to measure a second electrical property proportional to a current flowing through the drive coil as a function of time while the generated magnetic flux interacts with at least a portion of the target. The second sensing element can also be configured to generate a second signal based upon the second electrical property measurement. The controller can be in electrical communication with the magnetostrictive sensor. The controller can also be configured to receive the first and second signals and to determine a gap compensation signal based upon a function of the first signal and the second signal.

In another embodiment, the magnitude of the first signal and the magnitude of the second signal can change in the same direction in response to variation of a gap between the drive coil and the target.

In another embodiment the magnitude of the first signal and the magnitude of the second signal can change in opposite directions in response to circumferential variation of magnetic properties of the rotating target.

In another embodiment, the controller can be further configured to apply a predetermined gain to at least one of the first and second signals, prior to determining the gap compensation signal, and to determine the gap compensation signal based upon the sum of the first signal and the second signal after application of the predetermined gain.

In another embodiment, the predetermined gain can be selected such that, after application, the magnitude of respective portions of the first signal and modified second signals representing response of the measured first and second electrical properties to circumferential variation of magnetic properties of the rotating target are approximately equal to the magnitude.

In another embodiment, the magnetostrictive sensor can further include a sensing coil configured to output a stress signal characterizing a stress experienced by the rotating target. The stress signal can be based at least upon a measurement of the generated magnetic flux resulting from interaction of the first magnetic flux with the target.

In another embodiment, the controller can be further configured to receive the stress signal, to combine the stress signal with the gap compensation signal to yield a gap compensated stress signal, and to output the gap compensated stress signal.

In another embodiment, the stress can be a torque.

In another embodiment, the magnetostrictive sensor can include a sensor head including a driving pole and a sensing pole. The drive coil can be coupled to the driving pole and the sensing coil can be coupled to the sensing pole.

Methods for determining a gap-dependent signal exhibiting reduced sensitivity to electrical runout for use in gap compensation are provided. In one embodiment, the method can include generating, by a drive coil of a sensor, a magnetic flux in response to receipt of a current. The method can also include measuring, by a drive circuit, a first electrical property proportional to a voltage applied across the drive coil as a function of time while the generated magnetic flux interacts with at least a portion of a target. The method can further include measuring, by the drive circuit, a second electrical property proportional to a current flowing through the drive coil as a function of time while the generated magnetic flux interacts with at least the portion of the target. The method can additionally include receiving, by a controller, a first signal based upon the measured first electrical property and a second signal based upon the second measured electrical property. The method can also include determining, by the controller, a gap compensation signal based upon a function of the first signal and the second signal.

In another embodiment, the magnitude of the first signal and the magnitude of the second signal can change in opposite directions in response to circumferential variation of magnetic properties of the rotating target.

In another embodiment, the method can further include applying a predetermined gain to at least one of the first and second signals prior to determining the gap compensation signal, and determining the gap compensation signal based upon the sum of the first signal and the second signal after application of the predetermined gain. The predetermined gain can be selected such that, after application, the magnitude of the respective portions of the first signal and the second signal, representing response of the measured first and second electrical properties to circumferential variation of magnetic properties of the rotating target, are approximately equal in magnitude.

In another embodiment, the sensor can be a magnetostrictive sensor including a sensing coil configured to output a stress signal characterizing a stress experienced by the rotating target. The stress signal can be based at least upon a measurement of the generated magnetic flux resulting from interaction of the first magnetic flux with a target.

In another embodiment, the method can also include, by the controller, receiving the stress signal, combining the stress signal with the gap compensation signal to yield a gap-compensated stress signal, and outputting the gap-compensated stress signal.

In another embodiment, the magnetostrictive sensor can also include a sensor head including a driving pole and a sensing pole. The drive coil can be coupled to the driving pole and the sensing coil can be coupled to the sensing pole.

Magnetostrictive sensors are a type of sensor that can use magnetic signals to measure stress (e.g., torque) applied to a shaft. However, a magnetostrictive stress sensor can be highly sensitive to changes in the gap distance between itself and the shaft. If the gap distance changes while it makes stress measurements, which can occur due to vibrations, the change in gap distance can introduce error into the stress measurements. To reduce such error and improve the quality of the stress measurements, some existing sensors can measure changes in the gap distance to adjust the torque measurements. Due to variations in the magnetic properties of the shaft, it can be difficult to measure the gap distance accurately. Accordingly, improved techniques for determining gap changes are provided for use with magnetostrictive stress sensors to enhance the accuracy of stress and/or torque measurements, by compensating for gap changes as well as variation in magnetic properties of the shaft.

Embodiments of sensing systems and corresponding methods for gap-compensation of stress measurements acquired for rotating machine components are discussed herein. In certain embodiments, torque measurements can be obtained from the stress measurements and the geometry of the target (e.g., a shaft). However, embodiments of the disclosure can be employed to perform gap-compensation of any stress applied to rotating or stationary machine components without limit.

<FIG> illustrates one exemplary embodiment of an operating environment <NUM> containing a gap-compensated stress sensing system <NUM>, referred to herein as compensated stress sensing system <NUM>, and a target <NUM>. The compensated stress sensing system <NUM> can be a magnetostrictive stress sensing system including a sensor head <NUM>, a stress sensor <NUM>, and a controller <NUM> including a drive circuit <NUM> and one or more processors <NUM>. The stress sensor <NUM> can be positioned within the sensor head <NUM> and it can be configured to generate one or more stress signals <NUM> representative of stress applied to a selected portion of the target <NUM> as a function of time. The drive circuit <NUM> can be configured to supply a current I to the stress sensor <NUM> for generation of the stress signal <NUM>.

As discussed in greater detail below, the drive circuit <NUM> can be further configured to generate and output a plurality of signals <NUM> based upon measurement of electrical properties of the drive circuit <NUM>. The plurality of signals <NUM> can include a first signal based upon measurement of a first electrical property, proportional to a voltage applied across a driving coil of the stress sensor <NUM>, as a function of time. The first signal is also referred to herein as drive voltage DV. The plurality of signals <NUM> can also include a second signal based upon measurement of a second electrical property, proportional to the current I flowing through the driving coil of the stress sensor <NUM>, as a function of time. The second signal is also referred to herein as drive current DI.

It has been discovered that the magnitude of the drive voltage DV and the magnitude of the drive current DI do not respond in the same way to each of (a) variation in a gap G between the sensor head (e.g., a distal end 106d) and a surface of the target <NUM>, and (b) electrical runout. Instead, the magnitude of the drive voltage DV and the magnitude of the drive current DI change in the same direction (e.g., both increasing or both decreasing) in response to one of variation of the gap G and electrical runout. Furthermore, the magnitude of the drive voltage DV and the magnitude of the drive current DI change in opposite directions (e.g., one increasing and one decreasing) in response to the other of variation of the gap G and electrical runout. In either case, a function based upon the drive voltage DV and the drive current DI can be employed (e.g., by the processor <NUM>) to determine a gap-dependent reference signal <NUM> exhibits enhanced sensitivity to the gap G and reduced sensitivity to electrical runout. As discussed in detail below, in one embodiment, the function can be addition of the drive voltage DV and the drive current DI, or mathematical equivalents thereof. In another embodiment, the function can be subtraction of the drive voltage DV and the drive current DI or mathematical equivalents thereof. In general, the function is not limited to addition or subtraction. The function can include mathematical operations such as addition, subtraction, division, multiplication, logarithms, exponentiation, or trigonometric functions, alone or in any combination.

In one example, the magnitude of the drive voltage DV and the magnitude of the drive current DI can respond together with variation in the gap G, and can respond opposite to electrical runout. That is, the magnitude of each increases or decreases together in response to variation in the gap G, while one increases and the other decreases in response to electrical runout. In this scenario, the drive voltage DV and the drive current DI can be summed to obtain the gap-dependent reference signal <NUM>.

In another example, the magnitude of the drive voltage DV and the magnitude of the drive current DI can respond in opposite directions with variation in the gap G, and can respond in the same direction to electrical runout. That is, the magnitude of one increases and one decreases in response to variation in the gap G, while the magnitude of each increases or decreases together in response to electrical runout. In this scenario, the drive voltage DV and the drive current DI can be subtracted from one another to obtain the gap-dependent reference signal <NUM>.

In use, the sensor head <NUM> can be positioned proximate to the target <NUM> for acquiring stress measurements. The processor <NUM> can receive the measured stress signals <NUM> and the measured signals <NUM>. The gap-dependent reference signal <NUM> can be determined using the function of the measured signals <NUM>. The processor <NUM> can be further configured to employ the stress signals <NUM> and the gap-dependent reference signal <NUM> to determine an improved gap-compensated stress signal <NUM>, also referred to herein as a compensated stress measurement. The improved gap compensated stress signal <NUM> can represent a measurement of stress applied to the target <NUM> as a function of time which has reduced sensitivity to changes in the gap G, as compared to the stress signal <NUM>.

The compensated stress signal <NUM> can be subsequently output by the processor <NUM>. As an example, the compensated stress signal <NUM> can be received by one or more external devices <NUM>, such as a display for presentation to a user and/or a data storage device for storage and subsequent retrieval.

<FIG> is a side cross-sectional view of one exemplary embodiment of the compensated stress sensing system <NUM> in the form of compensated stress sensing system <NUM>. The compensated stress sensing system <NUM> includes a sensor head <NUM> in electrical communication with a controller <NUM>. The sensor head <NUM> can form a housing <NUM> that contains a magnetostrictive stress sensor including a core <NUM>, a drive coil <NUM>, and at least one sensing coil <NUM>. As discussed in greater detail below, the magnetostrictive stress sensor can be configured to output stress signals characterizing stress applied to a selected portion <NUM> of a target <NUM> (e.g., a portion of the target <NUM> positioned opposite the sensor head <NUM>). The controller <NUM> can be further configured to determine a gap-dependent reference signal that characterizes a gap <NUM> between the sensor head <NUM> (e.g., a distal end 206d of the housing <NUM>) and the selected portion <NUM> of the target <NUM> concurrently with the stress measurements acquired by the stress sensor. The gap-dependent reference signal can exhibit significantly reduced sensitivity to electrical runout of the target <NUM>, as compared with other techniques for acquiring gap-dependent measurements (e.g., eddy current proximity sensors).

The target <NUM> can be a component of any machine or equipment <NUM> that is configured to rotate. Examples of rotating components can include, but are not limited to, shafts and rotors. Examples of machines and equipment <NUM> incorporating rotating components can include, but are not limited to, turbomachines (e.g., turbine engines, compressors, pumps, and combinations thereof), generators, combustion engines, and combinations thereof. Stress can be applied to the target <NUM> by a driver <NUM> (e.g., a reciprocating engine, a combustion engine, a turbine engine, an electrical motor, etc.) to enable the target <NUM> to rotate and drive a load. The target <NUM> can be formed from materials including, but not limited to, ferromagnetic materials such as iron, steel, nickel, cobalt, and alloys thereof. In certain embodiments, the target <NUM> can be non-magnetized. In other embodiments, the target <NUM> can be magnetized.

The core <NUM> can include a base <NUM> and at least two elongated poles <NUM>, <NUM>. The poles <NUM>, <NUM> can extend outwards from the base <NUM> and they can be separated from one another by a selected distance. The core <NUM> can be formed from any ferromagnetic material. Examples can include, but are not limited to, iron, steel, nickel, cobalt, and alloys thereof. One of the poles <NUM> can be a driving pole to which the drive coil <NUM> is wrapped around. The other of the poles <NUM> can be a sensing pole to which the sensing coil <NUM> is wrapped around.

The drive coil <NUM> and the sensing coil <NUM> can each be in electrical communication with the controller <NUM>. As shown in <FIG>, the controller <NUM> can be electrically coupled to a drive circuit <NUM> by wired or wireless connections. Wireless communication devices, such as radio frequency (RF) transmitters, can be integrated with the controller <NUM> to transmit the signals to an RF receiver integrated with the drive circuit <NUM>. As also shown in <FIG>, the controller <NUM> can be positioned remotely from the sensor head <NUM>. However, in alternative embodiments (not shown), the controller <NUM> can be positioned within the sensor head <NUM>.

A power source <NUM> (e.g., electrical outlets, electrical generators, batteries, etc.) can provide power to the controller <NUM> and a drive circuit <NUM>. The drive circuit <NUM> can be configured to deliver a current <NUM> (e.g., an AC current) to the drive coil <NUM>. The controller <NUM> can be configured to control characteristics (e.g., frequency, amplitude, etc.) of the current <NUM>. The controller <NUM> can be any computing device employing a general purpose or application-specific processor <NUM>. In either case, the controller <NUM> can include memory <NUM> for storing instructions related to characteristics of the current <NUM>, such as frequency, amplitude, and combinations thereof. The memory <NUM> can also include instructions and algorithms for employing sensor signals (e.g., stress signal <NUM> and a gap-dependent reference signal) to determine gap-compensated stress measurements, as discussed in greater detail below.

The processor <NUM> can include one or more processing devices, and the memory <NUM> can include one or more tangible, non-transitory, machine-readable media collectively storing instructions executable by the processor <NUM> to perform the methods and control actions described herein. Embodiments of the controller <NUM> can be implemented using analog electronic circuitry, digital electronic circuitry, and/or combinations thereof.

The current <NUM> can pass through the drive coil <NUM> to generate a magnetic flux <NUM>. The magnetic flux <NUM> can permeate the target <NUM>, pass through the sensing coil <NUM>, and return to the drive coil <NUM> via the core <NUM> (e.g., the base <NUM> and the sensing pole <NUM>). In this manner, a magnetic loop can be formed through the stress sensor and the target <NUM>.

The sensing coil <NUM> can be used to measure the magnetic flux <NUM> exiting the target <NUM>. In general, stress (e.g., compression, tension, torque, shear, etc.) applied to the target <NUM> can change the magnetic permeability of the target <NUM>, which in turn can cause the magnetic flux <NUM> measured by the sensing coil <NUM> to change. Thus, a stress, such as torque, applied to the target <NUM> can be determined based on the change in magnetic flux <NUM> received by the sensing coil <NUM> relative to the magnetic flux <NUM> generated by the drive coil <NUM>. The sensing coil <NUM> can be configured to transmit the stress signal <NUM> to the controller <NUM> that is indicative of the changes (e.g., difference) in the magnetic flux <NUM>.

The stress signal <NUM> can be communicated by wired or wireless connections to the controller <NUM> (e.g., receiver <NUM>). As an example, wireless communication devices, such as RF transmitters, can be integrated with the sensor head <NUM> (e.g., proximate to the sensing coil <NUM>) to transmit the signals to a receiver <NUM> (e.g., an RF receiver) integrated with the controller <NUM>. The receiver <NUM> can optionally include electronic components (e.g., amplifiers, filters, etc.) that are configured to condition the stress signal <NUM> before transmission to the processor <NUM>.

As discussed above, the magnetic flux <NUM> measured by the sensing coil <NUM> can be affected by the gap <NUM>, which can extend between the distal end 206d of the housing <NUM> and a surface <NUM> of the target <NUM>, as well as electrical runout of the target <NUM> during rotation. Thus, stress measurements determined for the target <NUM> based upon the magnetic flux <NUM> sensed by the sensing coil <NUM> can deviate from the actual stress applied to the target <NUM>.

To address this issue, a plurality of electrical properties of the drive circuit <NUM> can be measured and corresponding signals can be output to the controller <NUM> as signals <NUM>. As discussed above, a first electrical property of the drive circuit <NUM>, proportional to the voltage applied across the drive coil <NUM>, can be measured as a function of time. A first signal based upon this first electrical property measurement, referred to herein as drive voltage DV, can be output to the controller <NUM>. A second electrical property of the drive circuit <NUM>, proportional to current flowing through the drive coil <NUM> can also be measured as a function of time. A second signal based upon this second electrical property measurement, referred to herein as drive current DI.

Embodiments of the first and second electrical properties can adopt a variety of configurations. As an example, the first and second electrical properties can be selected independently from any electrical property (e.g., voltage, current, resistance, inductance, capacitance, etc.) In one exemplary embodiment, the first and second electrical properties are each voltages.

The plurality of signals <NUM> can be communicated by wired or wireless connections to the controller <NUM> (e.g., receiver <NUM>). The receiver <NUM> can optionally include electronic components (e.g., amplifiers, filters, etc.) that are configured to condition the plurality of signals <NUM> before transmission to the processor <NUM>.

The memory <NUM> can include instructions and algorithms executable by the processor <NUM> to determine the gap-dependent reference signal, which is relatively insensitive to electrical runout, based upon the plurality of signals <NUM>. The memory <NUM> can also include instructions and algorithms executable by the processor <NUM> to determine, using the stress signals <NUM> and the gap-dependent reference signal, a gap-compensated stress measurement. In this manner, the accuracy of stress measurements output by the compensated stress sensing system <NUM> can be increased, enabling better control of the machine or equipment <NUM> incorporating the target <NUM>.

<FIG> is a top view of an exemplary embodiment of a core <NUM> of the sensor head <NUM> of the magnetostrictive stress sensor of <FIG>. As shown, the core <NUM> can include a cross axis yoke <NUM> having a cross yoke portion <NUM> and four bases 306a, 306b, 306c, 306d. The bases 306a, 306b, 306c, 306d can extend radially outward in a plane from the cross yoke portion <NUM> in any configuration and for any length that enables each to operate as described herein. The bases 306a, 306b, 306c, 306d can be angularly spaced apart by an angle ranging from about <NUM> degrees to <NUM> degrees (e.g., <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, <NUM> degrees, or any combination thereof). As shown in <FIG>, the bases 306a, 306b, 306c, 306d can be angularly spaced apart by approximately <NUM> degrees. Additional embodiments of the sensor head <NUM> are discussed in <CIT>, the entirety of which is hereby incorporated by reference.

<FIG> is a circuit diagram illustrating one exemplary embodiment of the drive circuit <NUM>, in the form of drive circuit <NUM>, in electrical communication with the drive coil <NUM>. As shown, the drive circuit <NUM> includes an excitation source <NUM>, a driver <NUM>, a sense resistance <NUM>, a first electrical property sensor <NUM>, and a second electrical property sensor <NUM>. The driver <NUM> and the sense resistance <NUM> can be in series with the excitation source <NUM> and the drive coil <NUM>. The first electrical property sensor <NUM> can be in parallel with the drive coil <NUM> and the second electrical property sensor <NUM> can be in parallel with the sensing resistor <NUM>.

In use, the power source <NUM> can be configured to provide electrical power to the excitation source <NUM>, and the excitation source <NUM> can be configured to generate current <NUM> (e.g., AC current) in response. Upon receipt of the current <NUM>, the drive coil <NUM> can generate the magnetic flux <NUM>.

Use of the sense resistance <NUM> within the drive circuit <NUM> can facilitate independent measurements of the voltage across the drive coil <NUM> and the current through the drive coil <NUM>. In one aspect, the first electrical property sensor <NUM> can be configured to output a first signal <NUM>, the drive voltage DV, that is based upon the first electrical property measurement. As noted above, the drive voltage DV can be proportional to voltage applied across the drive coil <NUM> as a function of time while the generated magnetic flux <NUM> interacts with at least a portion of the target <NUM> (e.g., the selected portion <NUM>). The second electrical property sensor <NUM> can be configured to output a second signal <NUM>, the drive current DI, that is based upon the second electrical property. As also discussed above, the drive current can be proportional to the current <NUM> flowing through the drive coil <NUM>.

In one embodiment, the first and second electrical properties can each be voltages. As an example, a first voltage can be measured by the first electrical property sensor across the drive coil <NUM> and a second voltage can be measured across the sense resistor <NUM> by the second electrical property sensor.

<FIG> is a plot of illustrating one embodiment of the first and second signals <NUM>, <NUM> output by the first and second sensing elements <NUM>, <NUM> (drive voltage DV and drive current DI, respectively) and received by the controller <NUM> (e.g., receiver <NUM>, processor <NUM>) for the first embodiment of the drive current DV and the drive voltage DI. The data are representative of the target <NUM> during rotation, with the amplitude of the first and second signals <NUM>, <NUM> plotted on the vertical axis and time plotted on the horizontal axis, each in arbitrary units (arb). In certain embodiments, regardless of the form of the first and second electrical properties, the first and second signals <NUM>, <NUM> can be provided to the controller <NUM> as a common electrical property (e.g., voltage, current, etc.), or converted by the controller <NUM>, for determining the gap-compensated reference signal.

As shown, the amplitude of the drive voltage DV and the drive current DI each demonstrate a repeated runout pattern 500a, 500b due to electrical runout of the target <NUM> (e.g., circumferential variation in the magnetic properties of the target <NUM>). Also shown are discrete vertical steps 502a, 502b, representing suspension of data collection while the gap is changed. As discussed above in regards to a first embodiment of the drive voltage DV and the drive current DI, the magnitude of the drive voltage DV and the magnitude of the drive current DI each change in the same direction (e.g., increasing) in response to the same variation in the gap <NUM>. Furthermore, the magnitude of the drive voltage DV and the magnitude of the drive current DI change in opposite directions in response to electrical runout.

In certain embodiments, a predetermined gain (e.g., a constant multiplier) can be applied to at least one of the signals <NUM>, <NUM>. The predetermined gain can be selected such that the magnitude of respective portions of the first and second signals <NUM>, <NUM> representing response of the measured first and second electrical properties (e.g., runout patterns 500a, 500b) are approximately equal in magnitude (e.g., within ±<NUM>% of one another).

As shown in <FIG>, the predetermined gain is applied to the second signal <NUM> alone (e.g., as a product), while the first signal <NUM> is unchanged. This yields a modified second signal <NUM>' having a runout pattern 500b' with a magnitude that is approximately the same as (e.g., within ±<NUM>% of) the magnitude of the runout pattern 500a. However, in alternative embodiments, a gain can be applied to the first signal alone, or to the first and the second signals in combination, so that the magnitudes of the runout patterns are approximately the same (e.g., within ±<NUM>% of one another). Subsequently, after application of the gain, the first and second signals <NUM> (e.g., the first signal <NUM> and the modified second signal <NUM>') can be summed to yield a gap-dependent reference signal <NUM>.

As an example, <FIG> reproduces the first signal <NUM> and the modified second signal <NUM>' along with their sum, representing the gap-dependent reference signal <NUM>. Because the magnitude of the drive voltage DV and the drive current DI respond in the same direction with the gap <NUM>, the gap-dependent reference signal <NUM> exhibits increased gap sensitivity. This is demonstrated by the large changes <NUM> in magnitude when the gap <NUM> is varied. Concurrently, because the magnitude of the drive voltage DV and the drive current DI respond in opposite directions with electrical runout, the gap dependent reference signal <NUM> exhibits significantly reduced runout sensitivity. This is demonstrated by the relatively small changes in magnitude within respective runout patterns <NUM>.

In further embodiments, application of the gain can be omitted. As an example, the sense resistor can be sized such that the magnitude of the runout patterns of the first signal and the second signal are approximately the same (e.g., within ±<NUM>% of one another). Subsequently the first and second signal can be summed to yield a gap-dependent reference signal.

With or without application of gain, a similar analysis can be performed for a second embodiment of the drive voltage DV and the drive current DI, where the magnitude of the drive voltage DV and the magnitude of the drive current DI respond in opposite directions with variation in the gap G, and respond in the same direction to electrical runout. Notably, however, because the response of the drive voltage DV and the drive current to the gap G and electrical runout in this second embodiments is opposite that of the first embodiment of the drive voltage DV and the drive current DI, the first and second signals can be subtracted to yield a gap-dependent reference signal.

<FIG> is a flow diagram illustrating an exemplary embodiment of a method <NUM> for determining the gap-dependent reference signal <NUM>. The method <NUM> can be further employed for determining improved, gap-compensated measurements of stress (e.g., torque) applied to a rotating target. The method <NUM> is described below in connection with the compensated stress sensing system <NUM> of <FIG>. As shown, the method <NUM> includes operations <NUM>-<NUM>. However, in embodiments of the method can include greater or fewer operations than illustrated in <FIG> and these operations can be performed in a different order than illustrated in <FIG>.

In operation <NUM>, the drive coil <NUM> of the sensor can generate magnetic flux <NUM> in response to receipt of the current <NUM> (e.g., from the drive circuit <NUM>). As an example, the sensor can be the magnetostrictive stress sensor including the core <NUM>, the drive coil <NUM>, and at least one sensing coil <NUM>.

In operation <NUM>, a first electrical property that is proportional to a voltage applied across the drive coil <NUM> (e.g., drive voltage DV) can be measured as a function time while the generated magnetic flux <NUM> interacts with at least a portion of the target <NUM> (e.g., the selected portion <NUM> of the target <NUM>). As an example, the first electrical property can be measured by the first electrical property sensor <NUM> of the drive circuit <NUM>, which is in parallel with the drive coil <NUM>.

In operation <NUM>, a second electrical property that is proportional to current flowing through the drive coil <NUM> can be measured as a function of time while the generated magnetic flux <NUM> interacts with the portion of the target <NUM>. As an example, the second electrical property can be measured by the second electrical property sensor <NUM> of the drive circuit <NUM>.

In operation <NUM>, a first signal (e.g., <NUM>) based upon the measured first electrical property and a second signal (e.g., <NUM>) based upon the measured second electrical property can be received by a controller (e.g., processor <NUM> of controller <NUM>).

Optionally, in operation <NUM>, the controller (e.g., the processor <NUM>) can apply a predetermined gain to at least one of the measured first and second signals. In one embodiment, the gain can be applied to the second signal <NUM>) to yield a modified second signal <NUM>'). The predetermined gain can be selected such that, after application, the magnitude of the respective portions of the first and second signals representing response of the measured first and second electrical properties to circumferential variation of magnetic properties of the rotating target (e.g., electrical runout), are approximately equal in magnitude (e.g., within ± <NUM>% of one another).

In alternative embodiments, application of the predetermined gain can be omitted. For example, the sense resistor of the drive circuit can be configured such that the magnitude of the respective portions of the first and second signals representing response of the measured first and second electrical properties to circumferential variation of magnetic properties of the rotating target (e.g., electrical runout), are approximately equal in magnitude (e.g., within ± <NUM>% of one another).

In operation <NUM>, the controller <NUM> (e.g., the processor <NUM>) can determine a gap compensation signal (e.g., the gap-dependent reference signal <NUM>) based upon a function of the first signal <NUM> and the second signal (either the second signal <NUM> without application of the predetermined gain or the modified second signal <NUM>' with application the predetermined gain.

As discussed above, in one embodiment of the drive voltage DV and the drive current DI, a magnitude of the drive voltage DV and the magnitude of the drive current DI change in the same direction in response to variation of a gap (e.g., gap <NUM>) between the drive coil <NUM> and the target <NUM>. Concurrently, the magnitude of the drive voltage DV and the magnitude of the drive current DI change in opposite directions in response to circumferential variation of magnetic properties (e.g., electrical runout) of the rotating target <NUM>. As a result, the gap-dependent reference signal can be obtained from summation of the first signal <NUM> and the second signal <NUM> (or modified second signal <NUM>').

As further discussed above, in another embodiment of the drive voltage DV and the drive current DI, a magnitude of the drive voltage DV and the magnitude of the drive current DI change in the opposite direction in response to variation of a gap (e.g., gap <NUM>) between the drive coil <NUM> and the target <NUM>. Concurrently, the magnitude of the drive voltage DV and the magnitude of the drive current DI change in the same direction in response to circumferential variation of magnetic properties (e.g., electrical runout) of the rotating target. As a result, the gap-dependent reference signal can be obtained from subtraction of the first signal and the second signal (or modified second signal).

In general, the gap dependent reference signal can be obtained from a function of drive current DI and drive voltage DV that includes mathematical operations such as addition, subtraction, division, multiplication, logarithms, exponentiation, or trigonometric functions, alone or in any combination.

The resulting gap-dependent reference signal can exhibit enhanced sensitivity to changes in gap G and substantially reduced sensitivity to electrical runout. That is, the runout pattern of the first signal and the runout pattern of the second signal (or modified second signal) can approximately cancel one another.

In further embodiments, the controller <NUM> (e.g., the processor <NUM> can be configured to receive a stress signal from the sensor and combine the stress signal with the gap compensation signal to yield a gap-compensated stress signal, and output the gap-compensated stress signal. In alternative embodiments, the stress signal can represent other stress (e.g., tension, compression, shear) applied to the target.

Exemplary technical effects of the methods, systems, and devices described herein include, by way of non-limiting example determination of a gap-dependent reference signal that is sensitive to changes in a gap between a magnetostrictive sensor and a target, and is relatively insensitive to electrical runout. The gap-dependent reference signal <NUM> can be employed to acquire a measurement of stress applied to the target that is substantially insensitive to changes in gap.

Certain exemplary embodiments have been described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems, devices, and methods disclosed herein. One or more examples of these embodiments have been illustrated in the accompanying drawings. Those skilled in the art will understand that the systems, devices, and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

Claim 1:
A system (<NUM>) for gap-compensated stress sensing, the system comprising:
a magnetostrictive sensor (<NUM>) including a drive coil (<NUM>) configured to generate a magnetic flux in response to receipt of a current and a sensing coil (<NUM>) configured to output a stress signal (<NUM>,<NUM>) characterizing a stress experienced by a rotating target (<NUM>), wherein the stress signal is based at least upon a measurement of the generated magnetic flux resulting from interaction of the magnetic flux with the target (<NUM>),
a drive circuit (<NUM>) in communication with the drive coil (<NUM>) and configured to provide the current, the drive circuit (<NUM>) characterized by including,
a first sensing element (<NUM>) in parallel with the drive coil (<NUM>) and configured to,
measure a first electrical property proportional to a voltage applied across the drive coil (<NUM>) as a function of time while the generated magnetic flux interacts with at least a portion of the target (<NUM>), and
generate a first signal (<NUM>) based upon the first electrical property measurement; and
a second sensing element (<NUM>) configured to,
measure a second electrical property proportional to a current flowing through the drive coil (<NUM>) as a function of time while the generated magnetic flux interacts with at least a portion of the target (<NUM>), and
generate a second signal (<NUM>) based upon the second electrical property measurement; and
a controller (<NUM>) in electrical communication with the magnetostrictive sensor (<NUM>), the controller (<NUM>) being configured to receive the first and second signals (<NUM>,<NUM>), and to determine a gap compensation signal (<NUM>,<NUM>) based upon a function of the first signal (<NUM>) and the second signal (<NUM>), wherein the gap is between the drive coil (<NUM>) and the target (<NUM>).