Torque measurement system (TMS) with improved accuracy

Abstract

Disclosed is a torque measurement system configured to determine produced torque using corrections factors based on calibration of the torque measurement system and a method suitable for characterizing the behavior of a TMS when torque is applied at representative speeds.

Description

Torque Measurement System (TMS) with Improved AccuracyCROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application No. 63 / 600,936 filed on November 20, 2023, which is incorporated herein.BACKGROUND

[0002] Modem turbine engines are capable of producing high torque values. Management of the torque output is essential to protecting gearboxes and aircraft structure from damage due to over-torque events. Additionally, modern engine management controls can utilize monitored torque values to enhance the efficient operations of high torque producing engines. Thus, improved accuracy in the measurement and monitoring of torque output will improve overall engine operation and enhance the longevity of associated equipment such as gearboxes and other driven devices.

[0003] Methods for torque measurement using variable reluctance (VR) sensors to measure twist across a shaft segment are well-known. Typically, a reference tube is used in conjunction with ferrous targets to assess twist across a length of shaft. Variable reluctance (VR) sensors are employed to measure changes in the timing of pulses produced by the passage of the ferrous targets. Twist in the shaft can be related to the relative change in pulse timing. Then, by knowing the torsional spring rate of the shaft, torque can be derived from twist.

[0004] The industry would benefit from the provision of a light weight and minimally invasive system capable of accurately measuring twist on a rotating shaft as well as multi-axis shaft motion. Monopole VR sensor-based solutions are light weight and minimally invasive but have limitations in terms of provided twist measurement accuracy. The best currently available systems have accuracies of 5-10% of full scale torque. They also use long (approximately 2 foot long) shafts (also called couplings or torque tubes). The present disclosure provides an improvement in accuracy of the torque measurement system by characterizing the behavior of the system through application of torque at representative speeds. In particular, use of a torque-at-speed calibration map produced by calibration testing at representative torque-at-speed conditions will improve torque measurement accuracy with improved integration (shorter torque tubes or couplings).SUMMARY

[0005] A torque measuring system comprising a coupling shaft with a plurality of targets and at least one target sensor positioned a predetermined distance from the plurality of interleaved targets. The TMS further includes at least one database containing calibration data and a signal conditioning unit in data communication with the at least one target sensor. The signal conditioning unit is configured to receive data from the target sensor and further configured to calculate raw twist of the coupling shaft and to calculate coupling shaft rotational speed. The signal conditioning unit is further configured to use the calibration data and calculated coupling shaft rotational speed to provide a calculated torque-at-speed compensated twist value. Additionally, the signal conditioning unit is configured to use the calculated torque-at-speed compensated twist value to calculate a final coupling shaft torque value.

[0006] The present disclosure also provides a calibrated torque measuring system comprising a coupling shaft with a plurality of interleaved targets; at least one target sensor positioned a predetermined distance from the plurality of interleaved targets; at least one database, the database containing calibration data, the calibration data including zerocal data, torque at speed data and coupling stiffness data; and, a signal conditioning unit, the signal conditioning unit in data communication with the at least one target sensor. The signal conditioning unit includes programming configured to use data from the at least one target sensor to provide a calculated raw twist of the coupling shaft value and to provide a calculated coupling shaft rotational speed value. Additionally, the programming is also configured to use the zerocal data and calculated coupling shaft rotational speed value to provide a calculated zerocal compensated twist value. Further, the programming is further configured to use the calculated zerocal compensated twist value, the torque at speed data, and the calculated coupling shaft rotational speed value, to provide a calculated final torque at speed corrected twist value. Finally, the programming is further configured to utilize the calculated final torque at speed corrected twist value and the coupling stiffness data to provide a calculated shaft torque value for the coupling shaft to be output by the signal conditioning unit.

[0007] A torque measuring system comprising a coupling shaft with a plurality of interleaved targets and at least one target sensor positioned a predetermined distance from the plurality of interleaved targets. The TMS also includes a temperature sensor, at least one database containing calibration data, a signal conditioning unit in data communication with the at least one target sensorand the temperature sensor. The signal conditioning unit including a zero-crossing detection circuit configured to receive a voltage signal produced by the at least one target sensor and a microcontroller configured to receive data from the zero-crossing detection circuit and the temperature sensor. Additionally, the microcontroller is configured to calculate the raw twist of the coupling shaft, the coupling shaft rotational speed, and a radial motion parameter between the coupling shaft and the at least one target sensor. The microcontroller is further configured to use the calibration data, the calculated coupling rotational speed, the radial motion parameter and data received from the temperature sensor to provide a calculated torque-at-speed compensated twist value. The microcontroller is also configured to use the calculated torque-at-speed compensated twist value with the stored coupling shaft stiffness data to calculate a final coupling shaft torque value to be output by the signal conditioning unit.

[0008] Further, the present disclosure provides a for calculating the torque applied to a coupling shaft. The method comprising: providing a torque measuring system, the torque measuring system comprising: the coupling shaft; a plurality of interleaved targets carried by the coupling shaft; a first target sensor positioned to monitor the plurality of interleaved targets; providing a database, the database containing calibration data including zerocal data, torque at speed data and coupling stiffness data; providing a signal conditioning unit, the signal conditioning unit in data communication with the first target sensor, wherein the signal conditioning unit includes programming configured to: use data from the first target sensor to calculate a coupling shaft rotational speed value; use data from the first target sensor to calculate a raw twist value of the coupling shaft, the signal conditioning unit; use the calibration data and the coupling shaft rotational speed value to provide a calculated zerocal compensated twist value; use the calculated zerocal compensate twist value, the torque at speed data and the coupling shaft rotational speed value to provide a final torque at speed corrected twist value;utilize the final torque at speed corrected twist value and the coupling stiffness data to provide a calculated shaft torque value for the coupling shaft; upon rotation of the coupling shaft, the target sensor generates a data signal; the signal conditioning unit receiving the data signal from the target sensor; and, in response to the data signal received from the target sensor, the signal conditioning unit uses the programming and the calibration data to determine the coupling shaft rotational speed value, the raw twist value of the coupling shaft, the calculated zerocal compensated twist value, the final torque at speed corrected twist value, to provide the calculated shaft torque value for the coupling shaft; the signal conditioning unit provides the calculated shaft torque value for the coupling shaft as an output value.

[0009] Additionally, the present disclosure provides a method for calculating the torque applied to a coupling shaft. The method comprises: storing zerocal calibration data within the at least one database; storing torque-at-speed calibration data within the at least one database; rotating a coupling shaft, the coupling shaft having a plurality of interleaved targets; positioning at least one target sensor a predetermined distance from the interleaved targets; using a signal conditioning unit to monitor voltage signals received from the at least one target sensor; in response to the received voltage signals calculate a raw twist for the coupling shaft and a coupling rotational shaft speed for the coupling shaft; using programming within the signal conditioning unit and the raw twist value and the calculated coupling rotational shaft speed to provide a calculated torque-at-speed compensated twist value for the coupling shaft; using programming within the signal conditioning unit and the calculated torque- at-speed compensated twist value to calculate a final coupling shaft torque value.

[0010] Further, the present disclosure provides a method for calculating the torque applied to a coupling shaft. The disclosed method comprises: storing zerocal calibration data within the at least one database; storing torque-at-speed calibration data within the at least one database;storing coupling shaft stiffness data within the at least one database; rotating a coupling shaft, the coupling shaft having a plurality of interleaved targets; positioning at least one target sensor a predetermined distance from the interleaved targets; using the signal conditioning unit to monitor voltage signals received from the at least one target sensor; in response to the received voltage signals calculate a raw twist for the coupling shaft and a coupling rotational shaft speed for the coupling shaft; in response to the received voltage signals calculate a radial motion parameter which corresponds to changes in distance between the interleaved targets and the at least one target sensor during rotation of the coupling shaft; using programming within the signal conditioning unit calculate a zerocal compensated twist value with input in the form of the calculated coupling rotational shaft speed and stored zerocal calibration data; using programming within the signal conditioning unit and the calculated zerocal compensated twist value, the calculated coupling rotational shaft speed, the radial motion parameter and the stored torque-at-speed calibration data to calculate a torque-at-speed value compensated for twist of the coupling shaft; providing data from a temperature sensor to the signal conditioning unit, the temperature sensor positioned to monitor a temperature of the coupling shaft; using programming within the signal conditioning unit and the data from the temperature sensor, the torque-at-speed value compensated for twist of the coupling shaft and the stored coupling shaft stiffness to calculate a final coupling shaft torque value.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG 1 provides a block diagram of a single channel torque measurement system (TMS).

[0012] FIG. 2 provides an example of a torque measurement system (TMS) rotating coupling and VR sensor components.

[0013] FIG. 3 illustrates an exploded view of the shaft assembly with twist section and cylinders with interleaved targets lined up for assembly.

[0014] FIG. 4 shows an example VR sensor output signal with logic level transitions at negative zero crossing and corresponding timer counts (vk).

[0015] FIG. 5 is a schematic for VR sensor signals being processed by the signal conditioning circuit and then read by the microcontroller.

[0016] FIGS. 6A and 6B illustrate the radial and tangential motion of a VR sensor relative to the interleaved targets.

[0017] FIG. 7 is a schematic showing the relative change in sensor position due to relative motion along the radial and tangential directions.

[0018] FIG. 8 is a flowchart showing steps applied by SCU programming for zerocal correction and torque-at-speed correction, with temperature but without radial motion correction, to provide final twist and corresponding shaft torque for a TMS with single or dual VR sensors.

[0019] FIG. 9 is a flowchart showing steps applied by SCU programming for torque-at-speed correction with temperature and radial motion correction to calculate final twist and corresponding shaft torque for TMS systems with dual VR sensors.

[0020] FIG. 10 shows a block diagram for a torque-at-speed calibration map generation apparatus using an aircraft engine or motor.

[0021] FIGS. 11 A, 1 IB and 11C provide examples of torque-at-speed calibration maps at two different speeds and including radial motion correction.

[0022] FIG. 12A is a diagram showing an example dual sensor DAB zerocal map (DABo).

[0023] Figure 12B is a flowchart showing process steps for creating a single sensor (ABo) or dual sensor (DABo) zerocal map.

[0024] FIG. 13A is a plot showing the raw, zerocal -applied, and zerocal-applied and torque- at-speed corrected and radial motion corrected dual sensor twist measurements (DAB) along with the actual twist in the coupling.

[0025] FIG. 13B provides a close-up of the final and actual data points for the region identified in FIG. 13 A.

[0026] FIG 14A is a plot of the full-scale torque measurement error percentage over a range of shaft speeds and applied torques for dual sensor twist measurement with correction for zerocal but lacking actual twist, speed, or radial motion corrections.

[0027] FIG. 14B provides a histogram depicting the corresponding error distribution and standard deviation for the values of FIG. 14A.

[0028] FIG 15 A depicts the capabilities of the prior art in the form of a plot of the full-scale torque measurement error percentage over a range of shaft speeds and applied torques for dualsensor twist measurement with correction for actual twist and zerocal but with no correction for speed, or radial motion.

[0029] FIG. 15B depicts a histogram of the error distribution and standard deviation for the values of FIG. 15 A.

[0030] FIG. 16A is a plot of the full-scale torque measurement error percentage over a range of shaft speeds and applied torques for dual sensor twist measurement with correction for zerocal twist offset, actual twist, and speed but without radial motion correction.

[0031] FIG. 16 B depicts a histogram of the error distribution and standard deviation for the values depicted in FIG. 16A.

[0032] FIG. 17A is a plot of the full-scale torque measurement error percentage over a range of shaft speeds and applied torques for dual sensor twist measurement with zerocal twist offset, actual twist, speed, and radial motion correction.

[0033] FIG. 17B depicts a histogram of the corresponding error distribution and standard deviation for the values of FIG. 17A.

[0034] FIG. 18A is a plot of the full-scale torque measurement error percentage over a range of normalized coupling shaft speeds and applied torques for single sensor twist measurement with zerocal twist offset, actual twist and speed correction but without radial motion correction.

[0035] FIG. 18B depicts a histogram of the corresponding error distribution and standard deviation for the values of FIG. 18 A.

[0036] FIG. 19 depicts measured stiffness resulting from application of torque.

[0037] FIG 20 is a flowchart showing steps applied by SCU programming for zerocal correction and torque-at-speed correction without temperature correction and without radial motion correction, to provide final twist and corresponding shaft torque for a TMS with single or dual VR sensors.DETAILED DESCRIPTION

[0038] The drawings included with this application illustrate certain aspects of the embodiments described herein. However, the drawings should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations,combinations, and equivalents in form and function, as will occur to those skilled in the art with the benefit of this disclosure.

[0039] The present disclosure may be understood more readily by reference to the following representative description. For simplicity and clarity of illustration, where appropriate, reference numerals may be repeated among the different figures to indicate corresponding or analogous elements. The following description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may have been exaggerated to better illustrate details and features of the present disclosure. Also, the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting except where indicated as such.

[0040] Throughout this disclosure, the terms “about”, “approximate”, and variations thereof, are used to indicate that a value includes the inherent variation or error for the device, system, or measuring method being employed as recognized by those skilled in the art.

[0041] The following abbreviations and terms are used in this disclosure.• a0, alta2, a3, a4, a5, a6, a7as, a^ example polynomial coefficients saved during calibration process for torque at speed• A, Bi, B2. Ci. C2 example polynomial coefficients saved during calibration process for zerocal• AB = Twist Delta in degrees between the A (104) and B (105) target sets measured by a single VR sensor• ABo : single VR sensor zerocal correction twist.• ABcai : single VR sensor twist, post zerocal correction.• ABcorr : single VR sensor twist correction for torque-at-speed.• ABfmai: single VR sensor final twist after correction for torque-at-speed.• fAB(co,T): zerocal function for single VR sensor• CPR = Counts per Revolution• DAB = Dual VR sensor twist measurement (in degrees) between the A and B interleaved targets.• DABraw: dual VR sensor measured twist, raw.DABo : dual VR sensor zerocal correction twist.DABcai : dual VR sensor twist, post zerocal correction.• DABcorr : dual VR sensor twist correction for torque-at-speed.• DABfmai: dual VR sensor final twist after correction for torque-at-speed.• fDAB(co,T): zerocal function for dual VR sensor• fdock = Clock_Frequency or high speed counter rate (counts / sec).• FS = Full Scale• h = nominal air gap between target wheel and VR sensor in radial direction• Kshaft: torsional stiffness of the TMS coupling shaft 100• g(T): calibration value of torsional stiffness of TMS coupling shaft as a function of temperature T• N = number of VR targets (A-side and B-side combined) per revolution.• R = nominal radius to target wheel• RAD = Radial Angular Distortion Timing delta, converted to degrees, between consecutive twist-invariant passes of two targets (i.e., the time between when an individual target passes the VRi sensor and when another target from the same side of coupling shaft 100 passes the VR2 sensor on the next timestep)• SCU = Signal Conditioning Unit• SPD = Normalized coupling shaft 100 speed expressed in degrees per clock count.• T : temperature.• TMS = Torque Measurement System• VR = Variable Reluctance• ZCD = Zero Crossing Detector• Zerocal = a twist offset calibration, that is a function of speed and, optionally, temperature, performed at zero torque• Vj , V2 : timing counter values at negative slope zero-crossing for sensor 1 and 2 respectively• co : measured coupling shaft 100 speed.• T: coupling shaft 100 torque.• Ax, Ay: change in position of VR sensor due to motion along x and y axes respectively.• Ah, A9: change in nominal air gap height and tangential angular position respectively due to radial motion along x and y axes of a VR sensor.

[0042] The present disclosure provides an improved torque measurement system 110 (TMS). TMS 110 incorporates improvements which enhance the accuracy of the torque calculations reported by TMS 110 as well as enable improved integration.

[0043] FIG. 1 shows a complete torque measurement system 110 including a coupling 10 with interleaved targets 103 at least one target sensor 102, an SCU 109, and optionally or additionally at least one temperature sensor 112. The coupling 10 is the rotating component while the sensors 102 are mounted around the interleaved targets 103, not shown in FIG. 1. Suitable target sensors for use in TMS 110, include but are not limited to, VR, eddy current, microwave, hall effect, optical including laser. Most embodiments of TMS 110 will use VR target sensors 102. TMS 110 also includes a zero cross detection circuit 130 within an SCU 109. Zero cross detection circuit 130 is configured to receive electrical signals from VR sensors 102.

[0044] One skilled in the art will recognize that boxes 140, 142 and 144 within SCU 109 represent databases suitable for storing data. Such databases may be separate, as shown, or a single data storage device configured to receive calibration data and mathematical operators, such as but not limited to polynomial coefficients, utilized by programming within microcontroller 132. Such databases may be located in or outside of SCU 109. The SCU 109 also contains a programmable microcontroller 132 with programming which utilizes the zero cross timing data to calculate the raw twist (box 146) and the rotational shaft speed co (box 147) of shaft 100. In another embodiment, SCU 109 includes programming suitable for determining zero cross timing in microcontroller 132 by sampling the waveform generated by VR sensor 102 comparing the waveform to the microcontroller’s internal timing. The programming of microcontroller 132 will follow the steps outlined in either FIGS. 8, 20 or FIG. 9 depending on the configuration of TMS 110. Additionally, if two or more VR sensors 102 are present in the system, then microcontroller 132 will also include programming suitable for calculating a radial motion dependent parameter (box 148) using the zero crossing timing data. The configuration of SCU 109, zero cross detection circuit 130 and microcontroller 132 represent one embodiment of TMS 110 for carrying out the following methods. SCU 109 may be arranged in alternative configurations using differing circuitry, data storage arrangements as well as alternatives to microcontroller 132. Therefore,reference to the performance of certain steps by SCU 109 also includes functionality carried out using zero cross detection circuit 130 and / or microcontroller 132.

[0045] To aid in the understanding of one physical configuration of TMS 110, FIG. 2 and FIG.3 show a rotatable TMS coupling 10 with a twist element 101, i.e., a compliant region of the coupling shaft 100, that undergoes enough twist under operational torque levels to be detected by the following method. VR sensors 102 are housed in a sensor cradle 111 structure, not shown, which retains VR sensors 102 in a fixed position. Thus, sensor cradle 111 and VR sensors 102 do not rotate with coupling shaft 100. Interleaved shaft targets 103 are part of or are attached to the rotating coupling shaft 100 or a flange carried by rotating coupling shaft 100 such that they are not in the primary torque transmission path through coupling shaft 100. A side targets 104 are on one side of the twist element 101 and the B side targets 105 are on the other side of shaft twist element 101. At least one non-contact variable reluctance sensor 102 is positioned such that the passing of targets 103 will induce an oscillating voltage waveform (see FIG. 4) with one voltage oscillation corresponding to each target 103 passing by the VR sensor 102. Thin-walled coupling shaft 100 with twist element 101 is commonly used in the art in connection with variable reluctance-based torque sensors 102. Rotation of coupling shaft 100 is around the z-axis defined by the coordinate system 108. In one embodiment, coupling shaft 100 carries input / output flanges or connection points 106 used to transmit torque from one drive train element to another.

[0046] An exemplary embodiment of TMS coupling 10 is illustrated in FIG. 3. In this example, A-side targets 104 are carried by a first cylinder element 150 and B-side targets 105 are carried by a second cylinder element 160. First cylinder element 150 is secured to mounting surface 152 and second cylinder element 160 is secured to mounting surface 162. Mounting surfaces 152 and 162 are on either side of twist element 101. Thus, as described above, interleaved targets 103 (A-side 104, B-side 105) are secured to opposing sides of twist element 101.

[0047] FIG. 4 shows an example voltage signal produced by VR sensor 102 due to passage of targets 103 below it as represented in plot A. The change of magnetic flux density between a single ferrous target 103 followed by an air gap results in the oscillatory change in voltage.

[0048] The method of using TMS 110 will be described with continued reference to the FIGS. Prior to using TMS 110 under operational conditions on an aircraft or other field operation, databases 140, 142, 144, utilized by microcontroller 132, must be prepopulated with zerocal, torque-at-speed and coupling shaft stiffness data. Population of these databases can be achievedusing engines on test stands under varying controlled conditions or on an aircraft. Regardless of the test environment, pre-population of databases 140, 142 and 144 will follow the same operational protocols described herein. When populating database 140, the zerocal data can be obtained by operating the shaft 100 under zero torque conditions while measuring the apparent twist of the shaft. Thus, the zerocal calibration data in database 140 represents a combination of the target-to-target variation in mechanical dimensions between the interleaved targets and the behavior of the VR sensor circuitry as a function of shaft speed and temperature measured under zero torque conditions. Methods for determining the zerocal calibration data are described in more detail below.

[0049] Following population of databases 140, 142 and 144, during operation of TMS 110, microcontroller 132 will use the stored zerocal data (box 140) along with calculated shaft speed 147 and a temperature sensor measurement provided by temperature sensor 112 to calculate zerocal compensated twist (box 141) from the raw twist. Additionally, microcontroller 132 uses stored torque-at-speed calibration data (box 142) along with calculated shaft speed to calculate torque-at-speed corrected twist (box 143). When TMS 10 has two or more VR sensors 102, microcontroller 132 may utilize the radial motion parameter (box 148) to provide a torque-at speed correction producing a more accurate value of twist measurement. The calibration torque-at-speed data represents the mechanical effects of torque applied to the shaft 100. Finally, microcontroller 132 utilizes stored shaft stiffness calibration data (box 144) in combination with the torque-at- speed corrected value of twist to calculate an accurate value of shaft torque (box 145). Thus, SCU 109 uses microcontroller 132 to output the calculated values of shaft torque and rotational speed. Methods for obtaining the torque-at-speed calibration data and shaft stiffness calibration data are described below.

[0050] During operation of TMS 110, a signal conditioning unit (SCU) 109, shown in FIG. 5, equipped with a zero-crossing detection circuit 130 reads the voltage signal (FIG. 4, plot A) and produces logic level one (FIG. 4, plot B) whenever a negative (or falling) transition occurs at zero volts; the logic level resets to zero (FIG. 4, plot B) whenever an arming voltage level is reached. Note that the SCU 109 may be embedded within a larger electronic controller, for example, an engine controller or FADEC. A microprocessor, field programmable gate array (FPGA) or microcontroller 132, within SCU 109, reads the value of a free running counter whenever logic level transitions from zero to one. For the purposes of this disclosure, the term microcontroller isconsidered to include any suitable programmable device capable of being incorporated into SCU 109 and performing the necessary calculations. This timer value is referred to as vf as depicted in plot C of FIG. 4, where subscript n refers to the sensor number and k refers to the index of a specific timing measurement. In this instance, the specific timing event is the zero crossing event which corresponds to the period of time between two successive targets 103 passing a single VR sensor 102. The zero crossing event is indicated at vertical line ZCD in FIG. 4, plot A. Thus, the zero crossing event is always on the negative slope of the waveform depicted in FIG. 4, plot A. A consecutive series of timer values from the first of two VR sensors 102 would be denoted vk, vk+1, Vi+2, etc. Note: while the zero cross detection 130 is shown as a separate circuit in FIGS. 1 and 5, parts or all of the circuit could also be implemented within microcontroller 132.

[0051] With reference to FIGS. 1, 8 and 9, microcontroller 132 calculates the speed of rotation of the TMS coupling 10 in two steps (box 147). The first step computes the counts per revolution (CPR) based on the timing count from a single sensor, say number 1, and the number of targets N as follows:CPR = vk- vk~NIn the second step, the speed SPD in degrees per clock count is calculated from CPR as follows:The speed ® in revolutions per minute (RPM) is calculated using the system timing clock rate, fciock, and CPR as follows:60 X fciOck a> = -CPRAn example value of fciock could be 200xl06(i.e. 200 MHz).

[0052] When the signals from two sensors 102 are spaced such that one target from the A-side 104 passes a first VR sensor 102 at approximately the same time as a target from the B-side 105 passes the other VR sensor 102, the twist can be characterized with a speed-independent dualsensor A-to-B (DAS)' twist parameter. Before normalization, the A-to-B timing difference in counts, dabkis:where vkis the timing count from a first VR sensor 102 at timing step k, and vkis the timing count from a second VR sensor 102 at timing step k, and flip is a 1 or -1 which is used to rectify the signal if the mean dabkvalue of the previous two revolutions is below zero. If the waveform pulsesare not registered in a way so that the A-side and B-side target positions are known for a given time step, k, the sign of the twist (i.e., whether it is positive or negative twist) is unknown. This can be addressed by machining targets 103 such that there is a twist offset under zero torque greater than the maximum designed negative twist. In that case, the A-side and B-side position is known according to the sign, positive or negative, of dabk, and signal rectification can provide the appropriate twist value once the offset is accounted for. The speed-normalized twist, DAB™, averaged over the entire set of T targets and in degrees is:

[0053] For single sensor-based approach, twist measurement is made by comparing the timing difference between when the A-side targets pass a sensor to when the B-side targets pass the same sensor. Before normalization, the A-to-B timing difference in counts for the first VR sensor 102, abk, is:where vkis the timing count from first VR sensor 102 at timing step k, and vk~kis the timing count from the same first VR sensor 102 at timing step k-1. The absolute speed-normalized twist, AB, measured by sensor land averaged over the entire set of N targets and in degrees is:

[0054] The waveform varies in reaction to changes in the relationship of targets 104 and 105. During application of torque to a thin-walled twist element 100, twist can be identified by the shift in targets 104 and 105 relative to one another. The small deflections result in a small timing change between sequential values.

[0055] FIGS. 6A and 6B show views of the TMS 110 with twist element 100, interleaved targets 103, and VR sensors 102. FIG. 6A also provides a section view of variable reluctance sensors 102 mounted in proximity to interleaved targets 104 and 105. It also shows radial motion 114 that causes a change in the air gap 123 between interleaved targets 104, 105 and sensors 102. FIG. 6B shows a different view of the TMS coupling 10 with relative motion between sensors 102 and interleaved targets 104, 105 in the tangential direction 115. During operation of the engine 310, heat, vibration, and other stresses can cause shifting of the components in TMS 110. Relativemovement between the components can occur due to differences in thermal expansion between different metals used throughout an aircraft drivetrain. Manufacturing tolerances also provide a source of position variation between parts. Each TMS 110 will have slight differences from another TMS 110 due to stacking of tolerances as the various parts in the final assembled TMS 110 will have slightly different sizes within the accepted range of tolerances per manufacturing requirements. In fact, the stack-up of tolerances may result in substantial measurements in the radial 114 and tangential 115 directions between unique assemblies. Additionally, structural flexing may contribute to relative movement in the radial 114 and tangential 115 directions. Thus, the construction limitations of TMS 110 will also produce tangential and radial shifts of variable reluctance sensors 102 with respect to coupling 10. In FIG. 6A, shift of variable reluctance sensors 102 in the radial direction is reflected by arrows 114 and in FIG. 6B, shift of variable reluctance sensors 102 in the tangential direction is reflected by arrows 115.

[0056] FIG. 7 illustrates how relative motion of the VR sensors 102 with respect to the TMS coupling 10 can produce a change in the radial air gap 123 as well as the tangential location of sensor(s) 102. Fig. 7 shows the nominal position 120 of a VR sensor 102 which is located at the sum of the nominal radius (R) 122 and nominal air gap (h) 123 from the centerline. Due to movement of the sensor in the local x-direction by Ax (124) and in the local y-direction by Ay (125), the final position 121 of sensor 102 is different from the nominal position 120. The final position 121 has a different air gap equal to the sum of the original air gap, h 123 and the change in the gap Ah 126, and new position tangentially shifted by A0, 127. This geometric analysis illustrates the need for including radial motion correction factors (RAD) to calculate an accurate value of final twist.

[0057] Changes to the radial air gap 123 and the angular spacing of the VR sensors 102 change the voltage waveforms of the VR sensors 102 and therefore change the timing of zero crosses which is reflected in the v1' values illustrated in FIG. 4. To compensate for these changes, a speed- normalized radial angular distortion (RAD) parameter is defined as follows (box 148):

[0058] FIG. 8 and FIG. 20 are flowcharts showing the program steps incorporated into microcontroller 132 to apply zerocal correction (ABo for single sensor or DABo for dual sensor) and torque-at-speed calibration (ABCon for single target sensor or DABCOIT for dual target sensor) to calculate final twist (ABfinaifor single target sensor or DABfmai for dual target sensor) andcorresponding shaft torque (T). FIG 20 includes the temperature sensor and compensation and Figure 8 does not. Using the SCU 109, the process starts with the detection of a series of negative sloped zero crossings of the two VR sensor signals by the SCU 109 and using those crossing event timer values, vk, through vk'N, to calculate shaft speed, co, and raw twist (ABrawfor a single target sensor or DAB™ for dual target sensors) of coupling shaft 100. In FIG 8, ,the corresponding zerocal value DABo is found by applying the DAB zerocal map FDAB(C ). . In FIG. 20, Using shaft temperature, T, which can be estimated using a temperature sensor 112 embedded in the cradle or some other local temperature sensor, the corresponding zerocal value DABo is found by applying the DAB zerocal map fDAB(co,T). The zerocal compensated twist DABcaiis calculated by subtracting the zerocal value, DABo, from the raw twist DABraw. The equations for the zerocal corrected values of twist are as follows:DABcai= DABraw — DABoABcal ABraw—ABfl where DABo and ABo are the zerocal values obtained from the stored zerocal calibration map (box 140) at measured shaft speed, co (as in FIG 8), or measured shaft speed and temperature, T (as in FIG 20). SCU 109 then applies the torque-at-speed map to calculate twist correction, DABCOrr. The numerical calculations can be performed using software written in a computing language suitable for the microprocessor 132 or SCU 109, such as C or Simulink. The final value of twist, DABfmai, is obtained by subtracting the twist correction, DABCOrr, from the zerocal corrected value, DABcai. SCU 109 calculates the torsional stiffness, Kshaft, corresponding to temperature, T. In FIG 8, the stiffness Kshaft is a single number. In FIG. 20, with knowledge of T, the stiffness, Kshaft, can be determined using a simple look-up table or a polynomial. The final shaft torque value (T) calculated by SCU 109 is the product of the torsional stiffness, Kshaft, and the final corrected value of twist, DAB final.

[0059] FIG. 9 is a flowchart showing the program steps incorporated into microcontroller 132 to apply zerocal correction (DABo) and torque-at-speed calibration (DABCOrr) with radial motion correction parameter RAD to calculate final twist (DABfmai) and corresponding shaft torque (T). Using the SCU 109, process starts with the detection of a series of negative zero crossings of the two VR sensor signals by the SCU 109 and using those crossing event timer values, vk, through vk’N, to calculate shaft speed co and raw twist DABraw of coupling shaft 100. Using shaft temperature T, which can be estimated using a temperature sensor 112 embedded in the cradle orsome other local temperature sensor, the corresponding zerocal value DABo is found by applying the DAB zerocal map foAB(ro,T). The zerocal compensated twist DABcaiis calculated by subtracting the zerocal value, DABo, from the raw twist DABraw. SCU 109 then calculates the radial motion parameter RAD using the negative zero-crossing values and then applies the torque- at-speed map to calculate twist correction DABcorr. The final value of twist DABfinaiis obtained by subtracting the twist correction DABcorr from the zerocal corrected value DABcai. The final shaft torque value (T) calculated by SCU 109 is the product of the torsional stiffness KShaft and the final corrected value of twist DABrinai.

[0060] FIG. 10 depicts an exemplary apparatus used during end-of-line testing of an engine or motor incorporating TMS 110 with SCU 109 to generate the torque-at-speed calibration maps. Typically, the end-of-line testing occurs at the final stage of manufacturing after TMS 110 is built and assembled but before it is used on a vehicle. The torque-at-speed calibration maps are created during end of line testing and are then stored in the SCU 109 for use in service on an engine. The setup includes an engine or drive motor 310, corresponding engine or motor controller 311, a calibrated dynamometer or brake 312 as the load, and the torque measurement system 110, all mounted on the same shaft 307. A reference torque transducer 303 may also be used to provide actual torque measurement. A control processor 206 is used to control the engine or drive motor 310 and dynamometer or brake 312 as well as received torque measurement information from the SCU 109 and optional reference torque transducer 303. Control processor 206 typically resides on a test computer (e.g., Windows personal computer). Engine or motor controller 311 is controlled by the control processor 206 to run the drivetrain at a commanded rotational speed © . The shaft torque T is measured by the TMS 110 using an SCU 109. The control processor 206 runs tests at different speed and torque combinations to generate a torque-at-speed map DABCOrr= fi (co , DABcai, RAD) for dual sensor correction with motion compensation or DABCOn = fz(co, DABcai) for dual sensor correction without motion compensation or ABCOrr= fs(©, ABcai) for single sensor correction without motion compensation. Example torque-at-speed calibration maps (fi) generated by this test apparatus at two different shaft speeds are shown in FIG. 11. The actual twist produced in the TMS 110 coupling is calculated from the measured torque and the torsional stiffness (Kshaft) of the coupling 10. Note: the test setup from FIG 10 is the nominal setup on the final engine or vehicle with the addition of the test equipment used by the Control processor 206 during the calibration of TMS 110. The additional equipment used during calibration includes a Reference torque transducer303 supported by a shaft 307 and a calibrated dynamometer if brake 312 also supported by shaft 307. The identified additional test equipment would not be present during normal operations.

[0061] The following paragraphs will describe operations suitable for populating database 140 of FIG. 1 with zerocal calibration data. The apparatus shown in FIG. 10 depicts one suitable apparatus for generating a “zerocal” correction map of twist variables (DABo, ABo) by running an engine or drive motor under no torque load i.e. “zero torque” conditions. In an idealized system, under zero torque, raw twist reading would be expected to be zero degrees. However, any timing offsets associated with the machining tolerances of the interleaved targets 103, VR sensor 102 behavior within the cradle 111, or the response of the VR circuitry 130 will result in an erroneous raw twist measurement that varies with speed and temperature. The zerocal map is a mathematical function of speed and, optionally, temperature that estimates this error, so that it can be subtracted from the raw twist measurements in operation. The zerocal map, therefore, includes physical inputs that affect the TMS 110 in the absence of torque. The control processor 206 can either dwell at each speed and optional temperature set point for a pre-determined duration, for example, 5 minutes, or slowly change values between the speed and temperature set points to re-create quasistatic behavior. Twist data is collected at these zero torque conditions by using the method for measuring the raw twist terms, DABraw or AB. This zero torque data is surveyed at a number of combinations of coupling temperature and speed, sufficient to fit a mathematical function, an example of which is shown in FIG. 12A.

[0062] FIG. 12B shows a flowchart suitable for implementing the DAB (dual VR sensor) zerocal map or AB (single VR sensor) zerocal map generation process. The zerocal map generation process can be performed on a single TMS system (called generic zero calibration calibration) or it can be performed on every TMS system produced. Sensor cradle 111, containing sensors 102, is positioned at the nominal design location over the interleaved targets 103 and within a suggested tolerance of 1 mil. An uninitialized zerocal map, which could be just a zerocal map with all values set to zero, is programmed onto the SCU 109. The control processor 206 communicates with engine or motor controller 311 and dynamometer or brake 312 to set the zero torque test conditions and receives measured twist data from the SCU 109 and optional reference transducer 303. Additionally, the desired test setpoints are loaded into control processor 206 as a test matrix for the zerocal procedure. Control processor 206 then iterates through all the engine or drive motor 310 set points. Processor 206 can either dwell at each test set point for a pre-determined duration,for example, 5 minutes, or slowly change values between the set points to re-create quasistatic behavior. The raw twist values (DABnw, ABraw) are calculated by the SCU 109 at each test set point and communicated to processor 206, along with corresponding measured shaft speed (co) and coupling temperature (T). After all the test points have been completed, a suitable fitting algorithm, e.g. the Levenberg-Marquardt non-linear least squares method, may be used to compute the coefficients of the DAB zerocal map, FDAB (co,T) or AB zerocal map, FAB (co,T), by fitting a mathematical function to the raw twist data. Levenberg-Marquardt is a popular alternative to the Gauss-Newton method of finding the minimum of a function (x) that is a sum of squares of nonlinear functions,Let the Jacobian of f x) be denoted J;(x), then the Levenberg-Marquardt method searches in the direction given by the solution p to the equations,where Xk are nonnegative scalars and I is the identity matrix. The method has the nice property that, for some scalar A related to k, the vector pk is the solution of the constrained subproblem of minimizingsubject to ||p||2 < A. (Gill, P. R; Murray, W.; and Wright, M. H."The Levenberg-Marquardt Method. " §4. 7.3 in Practical Optimization. London: Academic Press, pp. 1 6-137, 1981). FIG. 12A depicts an example of a DAB zerocal map produced according to the steps of FIG. 12B.The initial zerocal process described above provides a controlled test occurring at different conditions of shaft speed and temperature without application of torque. The DAB zerocal map for dual sensor twist (DAB) can be expressed as:DABo = foAB(®, T).Where: foAB = function co = speed, in RPMT = temperature in °CThe AB zerocal map for single sensor twist (AB) can be expressed as:ABo = fAB(®, T).Where:FAB = function© = speed, in RPMT = temperature in °C

[0063] An AB zerocal map or a DAB zerocal map, f (®,T), represented by FIG. 12A, could take different forms. One possible form is in polynomial form like f (co ,T) = A(1 + Bic + B2©2)(1 + CiT + C2T2), where A, Bi, B2, Ci and C2 are the coefficients calculated by a two-dimensional curve fitting algorithm.

[0064] An alternate format for generating and storing the zerocal map suitable for use in database 140 is a look-up table. In this format, the measured values of twist correction at zero torque are stored within the SCU (in box 140) along with the corresponding independent values of shaft speed (co) and coupling temperature (T). The microcontroller 132 would then use linear interpolation to calculate the twist correction (DABo or ABo) corresponding to intermediate measured values of shaft speed (co) and coupling temperature (T). The zerocal map in simplest form is just a single point, a twist offset, that is not a function of speed or ambient temperature.

[0065] TMS 110 may also be used to generate torque-at-speed calibration data for storage in database 142. The torque-at-speed data will typically be formatted as torque-at-speed maps generated under test conditions which apply torque-at-speed correction to the components of the TMS 110. Thus, under the following method, twist correction (DABcorr) is a function of shaft speed (co), estimated twist (DABcai) and radial motion (RAD) when tested under the application of torque. The zerocal compensated twist (DABcai) is calculated by subtracting the DAB zerocal map value from the raw calculated twist value: DABcai= DABraw- DABo. An example of the resulting torque-at-speed map produced at various RPMs is provided in FIGS. 11 A, 11B, and is of the following mathematical form for a dual sensor scheme with radial motion correction:DABcorr = fi(co, DABcai, RAD)Figure 11C shows an example torque-at-speed map for a dual sensor scheme without radial motion correction (i.e., DABcorr = fi(co , DABcai)).

[0066] The torque-at-speed map can have the following polynomial form for simple and flexible implementation in an embedded microcontroller: f(x,y, z) = a0+ a x + a2y +a3x2+ a4y2+ a5xy + a6z + a7z2+ a8zx + a9yz where x, y, z are independent variables and ao through a9 are constant coefficients. For dual-sensor torque-at-speed maps with radial correction, the independent variables would be x = ro, y = DABcaiand z = RAD. For a dual sensor torque-at-speed map without radial correction, the independent variables would be x = co and y = DABcaiwith coefficients ae, a?, as and a9 set to zero. For a single sensor torque-at-speed map, the independent variables would be x = co and y = ABcaiwith coefficients ae, a?, as and a9 set to zero. The polynomial coefficients are then stored within the SCU (box 142 for stored torque at speed calibration information) for use in the twist correction process described in FIG. 8 and FIG. 9.

[0067] An alternate format for generating and storing the torque-at-speed calibration map within database 142 is a look-up table. In this format, for a dual sensor scheme with radial motion correction, the actual values of twist correction (DABCOrr) are stored within the SCU (in box 142) along with the corresponding independent values of (DABeai), shaft speed (co) and radial motion parameter (RAD). The microcontroller 132 would then use linear interpolation to calculate the twist correction (DABcai) corresponding to intermediate measured values of (DABcai), shaft speed (co) and radial motion parameter (RAD).

[0068] One method of calculating the torsional shaft stiffness (Kshaft) of the TMS coupling 10 is by using computational methods, for example, finite element analysis (FEA) along with material properties of the coupling construction material, to the coupling mechanical model. The resulting shaft stiffness data is stored in database 144. An alternative method for providing the shaft stiffness data is to statically apply different levels of torque on a coupling and measure the corresponding twists on the shaft using displacement gages. Torsional stiffness (KShaft) is then calculated using the slope of a linear fit to the torque-twist data as depicted in FIG. 19. This test can be performed on a single coupling to produce a generic calibration or multiple couplings may be tested using this method to arrive at a statistically accurate estimate of torsional stiffness (Kshjtft). Using methods known to the art, the signals from a pair of optical encoders (not shown), positioned on each side of coupling 10, can be compared to determine the coupling twist. The twist can then be compared to the torque measured by the reference torque transducer 303 as described above to determine the torsional stiffness (Kshafi). Performing the torsional stiffness test at differenttemperatures can provide the torsional stiffness as a function of temperature thereby improving accuracy in applications where the coupling 10 temperature varies significantly. In that case, the temperature of the coupling 10 must be estimated or measured to update the Kshaft value (box 145) while operating the TMS 110. Use of temperature sensor 112 can provide an adequate estimate of the coupling 10 temperature for these purposes.

[0069] FIG. 13A shows the measured and corrected twist values from a dual sensor TMS 110 at various levels of applied torque and at different shaft speeds. The actual twist values, calculated by dividing the measured torque from an independent reference transducer 303 by the coupling stiff (Kshaft), is shown with symbol “x” in FIG 13A and close-up in FIG. 13B. The raw measured twist (DABraw), shown using circles, is corrected using the stored zerocal map (box 140), resulting in post-zerocal values (DABcai), shown using squares. This step (box 141) removes any effects of pre-machined targets offsets or effects of speed and temperature at zero torque conditions but does not compensate any torque-related effects. Though this step results in accurate values of measured torque at applied torques close to zero, the error increases significantly as more and more engine or brake torque is applied. In the next step (box 143), stored calibration data from torque-at-speed calibration (box 142) is used to calculate the necessary correction (DABcorr) due to applied torque and applied to calculate the final values of coupling twist (DABfmai), shown using diamond symbols. Thus, FIG. 13 A demonstrates the need for the additional calibration provided by addition of the torque-at-speed calibration method. As seen greater detail in FIG. 13B, the twist values obtained after torque-at-speed correction are very close to the actual values reported by a reference torque transducer 303. Note that the twist at full-scale torque is approximately 0.6 degrees. However, this system will function equally well with full-scale twist as low as 0.2 degrees. This is much smaller than the typical twist of existing torque systems that is 2 degrees or higher. This invention achieves high torque accuracy at low twist, which results in low overall shaft length (e g. 0.4 feet long versus 2 feet or longer). However, shaft lengths between 0.25 feet and 2 feet may also be used.

[0070] FIG. 14A shows the accuracy of TMS 110 measurement using dual VR sensors if only the speed-dependent zerocal twist correction (DABo) is applied to the raw twist. This step corresponds to box 141 from figure 1. As shown in FIGS. 14A and 14B, the torque measurement error could be up to 40% with significant spread in the measurements (9.81%). It is also observed that the torque measurement error (% of Full scale (FS) torque) increases with the applied torquelevels, which implies that an additional torque-based correction may be needed to improve accuracy.

[0071] FIG. 15A shows the torque measurement accuracy for a dual VR sensor system with twist offset and twist slope correction but no speed or radial motion considerations. The measurement errors can be up to ±7% and there is significant variation with applied torque levels (FIG. 15B).

[0072] FIG. 16A shows the torque measurement accuracy for a dual VR sensor system with speed-dependent zerocal correction to raw twist followed by torque-at-speed correction without radial motion effects, based on the flowchart shown in FIG. 8. The mathematical form for the twist correction from torque-at-speed calibration map is DABcorr = 1'2(01, DABcai). The maximum measurement errors can be up to 3.8% of FS torque with a standard deviation of 1.37%, as seen in FIG. 16B. This step is an improvement over the previous and corresponds to using the blocks 141 and 143 but not block 148 from FIG. 1.

[0073] FIG. 17A illustrates the torque measurement accuracy when using a dual VR-sensor based TMS with zerocal twist correction (box 141), twist correction from torque-at-speed calibration map (box 143) and additional radial motion correction (box 148), based on the flowchart shown in FIG. 9. The mathematical form for the twist correction from torque-at-speed calibration map is DABCorr = fi(co, DABcai, RAD). The error distributions in FIGS. 17A and 17B show that after application of the zerocal correction followed by a torque-at-speed correction including radial motion correction, most of the torque measurement error is limited to ±1% of FS torque with a standard deviation of 0.35%, which is more accurate than the other configurations, thus showing the significance of including all correction steps.

[0074] FIG. 18A shows the torque measurement accuracy for a single VR sensor system with speed-dependent zerocal correction to raw twist followed by torque-at-speed correction without radial motion effects. The mathematical form for the twist correction from torque-at-speed calibration map is ABCOrr= fi(®, ABcai). The maximum measurement errors can be up to 4.5% of FS torque with a standard deviation of 1.73%, as seen in FIG. 18B. Since the parameter RAD is calculated from the timing difference from two target sensors, it cannot be calculated and thereby not applied for a single sensor TMS configuration.

[0075] Other embodiments of the present invention will be apparent to one skilled in the art. As such, the foregoing description merely enables and describes the general uses and methods ofthe present invention. Accordingly, the following claims define the true scope of the present invention.

Claims

We claim:

1. A calibrated torque measuring system comprising: a coupling shaft with a plurality of interleaved targets; at least one target sensor positioned a predetermined distance from the plurality of interleaved targets; at least one database, the database containing calibration data, the calibration data including zerocal data, torque at speed data and coupling stiffness data; a signal conditioning unit, the signal conditioning unit in data communication with the at least one target sensor, the signal conditioning unit including: programming configured to use data from the at least one target sensor to provide a calculated raw twist of the coupling shaft value and to provide a calculated coupling shaft rotational speed value; wherein the programming is also configured to use the zerocal data and calculated coupling shaft rotational speed value to provide a calculated zerocal compensated twist value; wherein the programming is further configured to use the calculated zerocal compensated twist value, the torque at speed data, and the calculated coupling shaft rotational speed value, to provide a calculated final torque at speed corrected twist value; and, wherein the programming is further configured to utilize the calculated final torque at speed corrected twist value and the coupling stiffness data to provide a calculated shaft torque value for the coupling shaft to be output by the signal conditioning unit.

2. The calibrated torque measuring system of claim 1, further comprising: a temperature sensor; the stored calibration data additionally includes temperature compensation data for the coupling shaft stiffness data; wherein the SCU programming is further configured to use temperature compensation data to provide the calculated shaft torque value for the coupling shaft to be output by the signal conditioning unit.

3. The calibration torque measurement system of claim 2, where the coupling shaft stiffness data stored in the database comes from a finite element based model or a generic calibration of one or multiple shafts.

4. The calibrated torque measuring system of claim 1, further comprising: at least one temperature sensor; the stored calibration data additionally includes temperature compensation data for the zerocal data; wherein the SCU programming is further configured to use data from the temperature sensor to provide the calculated zerocal compensated twist value.

5. The calibrated torque measuring system of claim 1, further comprising: at least one temperature sensor; the stored calibration data additionally includes temperature compensation data for the coupling shaft stiffness data and the zerocal data; wherein the SCU programming is further configured to use data from the temperature sensor to provide the calculated zerocal compensated twist value; wherein the SCU programming is further configured to use temperature compensation data to provide the calculated shaft torque value for the coupling shaft to be output by the signal conditioning unit.

6. The calibrated torque measuring system of claim 1, further comprising: a second target sensor positioned a predetermined distance from the plurality of interleaved targets, the second target sensor in data communication with the signal conditioning unit; wherein the programming is further configured to calculate a radial motion parameter of the coupling shaft using the first and second target sensors; wherein the programming is further configured to use the radial motion parameter to provide the calculated final torque at speed corrected twist value.

7. The calibrated torque measuring system of claim 1, further comprising: a temperature sensor; a second target sensor positioned a predetermined distance from the plurality of interleaved targets; the stored calibration data additionally includes temperature compensation data;wherein the signal conditioning unit is configured to receive data from the temperature sensor and the second target sensor; wherein the programming is further configured to calculate a radial motion parameter between the coupling shaft and the at first and second target sensors; wherein the programming is further configured to use data from the first and second target sensors to provide the calculated raw twist of the coupling shaft value; wherein the programming is further configured to use the calibration data, the calculated coupling shaft rotational speed value and temperature sensor data to provide the zerocal compensated twist value; wherein the programming is further configured to use the radial motion parameter and the data from the temperature sensor to provide the calculated final torque at speed corrected twist value; wherein the programming is further configured to use temperature compensation data to provide the calculated shaft torque value for the coupling shaft to be output by the signal conditioning unit.

8. The calibrated torque measuring system of claim 1, wherein the programming is further configured to use the calculated zerocal compensated twist and the calculated coupling shaft rotational speed value to provide a calculated torque at speed correction value and, wherein the programming is further configured to use the calculated torque at speed correction value and the calculated zerocal compensated twist value to provide the final torque at speed corrected twist value.

9. The system of claim 1, where the final torque at speed corrected twist value is calculated from a polynomial function or look-up table of the calculated zerocal compensated twist and the calculated coupling shaft rotational speed.

10. The calibrated torque measuring system of claim 1, further comprising: a zero-crossing detection circuit configured to receive a voltage signal produced by the at least one target sensor; and, wherein the signal conditioning unit includes a microcontroller, the microcontroller is configured to receive data from the zero-crossing detection circuit and wherein the microcontroller includes the programming.

11. A method for calculating the torque applied to a coupling shaft, the method comprising:providing a torque measuring system, the torque measuring system comprising: the coupling shaft; a plurality of interleaved targets carried by the coupling shaft; a first target sensor positioned to monitor the plurality of interleaved targets; providing a database, the database containing calibration data including zerocal data, torque at speed data and coupling stiffness data; providing a signal conditioning unit, the signal conditioning unit in data communication with the first target sensor, wherein the signal conditioning unit includes programming configured to: use data from the first target sensor to calculate a coupling shaft rotational speed value; use data from the first target sensor to calculate a raw twist value of the coupling shaft, the signal conditioning unit; use the calibration data and the coupling shaft rotational speed value to provide a calculated zerocal compensated twist value; use the calculated zerocal compensate twist value, the torque at speed data and the coupling shaft rotational speed value to provide a final torque at speed corrected twist value; utilize the final torque at speed corrected twist value and the coupling stiffness data to provide a calculated shaft torque value for the coupling shaft; upon rotation of the coupling shaft, the target sensor generates a data signal; the signal conditioning unit receiving the data signal from the target sensor; and, in response to the data signal received from the target sensor, the signal conditioning unit uses the programming and the calibration data to determine the coupling shaft rotational speed value, the raw twist value of the coupling shaft, the calculated zerocal compensated twist value, the final torque at speed corrected twist value, to provide the calculated shaft torque value for the coupling shaft; the signal conditioning unit provides the calculated shaft torque value for the coupling shaft as an output value.

12. The method of claim 11 for calculating the torque applied to a coupling shaft, wherein:the torque measuring system further includes a temperature sensor and wherein the calibration data also includes temperature compensation data for the coupling shaft and the zerocal data; wherein the programming to provide the calculated zerocal compensated twist value also uses data from the temperature sensor to provide a temperature compensated zerocal compensated twist value; wherein the programming to provide the final torque at speed corrected twist value also uses data from the temperature sensor to provide the final torque at speed corrected twist value; wherein the programming to provide the final coupling shaft torque value also uses the temperature compensation data and provide the final coupling shaft torque value.

13. The method of claim 12 for calculating the torque applied to a coupling shaft, wherein: the torque measuring system includes a second target sensor positioned to monitor the plurality of interleaved targets, the second target sensor in data communication with the signal conditioning unit; wherein the signal conditioning unit further includes programming which uses the data from the first and second target sensors to calculate a radial motion parameter between the coupling shaft and the at first and second target sensors; wherein the programming to provide the calculated final torque at speed corrected twist value also uses the radial motion parameter; and, wherein the programming to provide the calculated shaft torque value for the coupling shaft also uses the radial motion parameter.

14. The method of claim 12 for calculating the torque applied to a coupling shaft, wherein: the torque measuring system further includes a temperature sensor, a second target sensor positioned to monitor the plurality of interleaved targets, the second target sensor in data communication with the signal conditioning unit; wherein the calibration data also includes temperature compensation data for the coupling shaft; wherein the programming for calculating the raw twist value of the coupling shaft, the signal conditioning unit uses data from the first and second target sensors;wherein the signal conditioning unit further includes programming which uses the data from the first and second target sensors to calculate a radial motion parameter between the coupling shaft and the first and second target sensors; wherein the programming to provide the calculated zerocal compensated twist value also uses data from the temperature sensor to provide a temperature compensated zerocal twist value; wherein the signal conditioning unit further includes programming which uses the temperature compensated zerocal compensated twist value and the raw twist value of the coupling shaft to provide a final zerocal compensated twist value; wherein the programming to provide the final torque at speed corrected twist value also uses the temperature compensated zerocal twist value and the radial motion parameter between the coupling shaft and the first and second target sensors to provide the final torque at speed corrected twist value; and, wherein the programming to provide the calculated shaft torque value for the coupling shaft also uses temperature compensated coupling shaft stiffness data.

15. The method of claim 12 for calculating the torque applied to a coupling shaft, wherein: the signal conditioning unit further includes programming which uses the calculated zerocal compensated twist and the calculated coupling shaft rotational speed value to provide a calculated torque at speed correction value and, wherein the programming to provide the final torque at speed corrected twist value also uses the calculated torque at speed correction value.

16. The method of claim 12 for calculating the torque applied to a coupling shaft, wherein: the torque measuring system further includes a zero-crossing detection circuit configured to receive a voltage signal produced by the at least one target sensor; and, wherein the signal conditioning unit includes a microcontroller, the microcontroller is configured to receive data from the zero-crossing detection circuit and wherein the microcontroller includes the programming.

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