Rotational torque measurement device

A device for measuring torque applied through a rotating member. A first torsion reference member is fixedly coupled to the rotating member at a first axial position and a second torsion reference member is fixedly coupled to the rotating member at a second axial position. A first detector detects the passage of the first torsion reference member past the first detector upon each full rotation of the rotating member and to generate a first signal upon each passage of the first torsion reference member. A second detector detects the passage of the second torsion reference member past the second detector upon each full rotation of the rotating member and to generate a second signal upon each passage of the second torsion reference member. A controller calculates a phase difference between the first signal and the second signal relative during rotation of the rotating member under a torsional load.

BACKGROUND

The present invention relates to a torque measurement device, and more particularly to a rotational torque measurement device with a reference member and detector.

Torque measurement devices typically utilize a torque transducer or sensor, which convert an applied torque into an electrical signal. A strain gauge is a torque transducer that converts applied torque into a change in electrical resistance. Typically, a strain gauge is attached to a deformable member, a torque is applied, and a change in electrical resistance is measured as the member deforms. The change in electrical resistance is converted into a torque measurement. Inertia of rotating components can cause measurement error. Additionally, due to their wires, such strain gauges are not applicable to rotating members.

SUMMARY

In one embodiment, the invention provides a device for measuring the torque applied through a rotating member rotating about a longitudinal axis, relative to a fixed member. The device includes a first torsion reference member fixedly coupled to the rotating member at a first axial position and a second torsion reference member fixedly coupled to the rotating member at a second axial position. A first detector is coupled to the fixed member and configured to detect the passage of the first torsion reference member past the first detector upon each full rotation of the rotating member and to generate a first signal upon each passage of the first torsion reference member. A second detector is coupled to the fixed member and configured to detect the passage of the second torsion reference member past the second detector upon each full rotation of the rotating member and to generate a second signal upon each passage of the second torsion reference member. A controller is configured to calculate a phase difference between the first signal and the second signal relative to a time reference during rotation of the rotating member under a torsional load. The controller compares the phase difference to a reference value and calculates a torque loading on the rotating member resulting from the torsional load based on the phase difference.

In another embodiment the invention provides a method of measuring torque applied through a rotating member rotating about a longitudinal axis relative to a fixed member. The method includes applying a torsional load to the rotating member. Rotation of the rotating member is detected at a first axial position and a first signal is generated. Rotation of the rotating member is detected at a second axial position and a second signal is generated. A loaded phase difference is calculated between the first signal and the second signal and compared to a reference value. A torque applied to the rotating member is calculated based at least upon the magnitude of loaded phase difference relative to the reference phase difference.

In yet another embodiment, the invention provides a system for calculating a torque load on a shaft. The system includes a first sensor generating a first signal in response to rotation of the first portion of the shaft and a second sensor generating a second signal in response to rotation of the second portion of the shaft. A processor compares the first signal to the second signal to arrive at a loaded phase difference between the first and second signals while the shaft is rotating under a load. The loaded phase difference is compared to a baseline phase difference. A twist in the shaft between the first and second portions of the shaft is calculated based on a difference between the loaded phase difference and the baseline phase difference.

DETAILED DESCRIPTION

FIG. 1is a perspective view of a shaft10. The shaft10has a torque T applied about an axis14, resulting in torsion illustrated generally at18. Torsion is the twisting of an object due to an applied torque. As indicated by the reference line22, the torsion18can be measured as an angular deformation26between a first axial position30(in this case, a first end) and a second axial position34(in this case, a second end). For a shaft of known mechanical characteristics, a magnitude of the applied torque can be calculated, derived or correlated by determining a change in torsion from a baseline or known value. As used herein, the torque T is not limited to numerical values expressed in the usual units of Newton-meters or foot-lbs, but may also express a comparative value from which the actual torque may be determined.

FIG. 2is a perspective view of the shaft10with a torque measurement device38according to one aspect of the invention. The shaft10is illustrated as being disposed within a fixed member42. The shaft10may be a rotor, turbine shaft, drive shaft, power take off or other rotating member. The fixed member42may be, for example, a motor, engine, or transmission housing. The fixed member42may also be a radial or thrust bearing, or any other member fixed relative to a rotating member. The shaft10is rotatably supported by the fixed member42about the axis14, for rotation with respect to the fixed member42.

A first torsion reference member46is fixedly coupled to the shaft10, for rotation with the shaft, at the first axial position30. A second torsion reference member50is fixedly coupled to the shaft10, for rotation with the shaft, at the second axial position34. Although the torsion reference members46and50are illustrated as being located at first and second ends of the shaft, respectively, the torsion reference members can be placed anywhere along the shaft so long as a distance L between the reference members is known. In the embodiment ofFIG. 1, each of the first torsion reference member46and the second torsion reference member50is a circular disk, though in other embodiments they may be triangular, square, star, or other polygonal shapes. The reference members46and50are oriented perpendicular to the axis14, concentric with the axis. In the embodiment ofFIG. 2, each reference member46and50includes a pattern of alternating light reflective areas54and light absorbing areas58arranged in a ring62concentric about the axis14.

A first detector (i.e., sensor)66is coupled to the fixed member42adjacent the first reference member46. A second detector70is coupled to the fixed member42adjacent the second reference member50. The detectors66and70in the embodiment ofFIG. 2are optical and substantially identical. In other embodiments, the first detector and the second detector may differ in form or function. As shown inFIG. 3, the detector66emits an emitted light74from an emitter portion78against the reference member46. The detector66receives reflected light82reflected off the reference member46at a receiver portion86.

Each detector66and70receives reflected light82when a light reflective area54passes in front of the detector and does not receive reflected light when a light absorbing area58passes in front of the detector. In this regard, it is not important in the broader scope of the invention that the areas between the light reflective area54be light absorbing per se. In other embodiments, the light absorbing area58may be replaced with an area that is light reflecting, but is angled such that the reflected light82does not reach the receiver portion86, and achieve the same purpose as the light absorbing area58. In other embodiments, the light absorbing area58could be reflective, but light scattering (e.g., a many faceted surface) and achieve the same purpose as the light absorbing area58. In some embodiments, the emitted and reflected light may be in the visible spectrum. In other embodiments, the light may be ultraviolet, infrared, or other ranges of the electromagnetic spectrum. The emitter portion may also be a laser. Similarly, the reflective areas and absorbing areas may be optimized for specific wavelengths of a corresponding detector.

Each detector66and70produces a signal with a first amplitude in response to receiving light at the receiver portion86, and a second amplitude in response to receiving no light or light of insufficient intensity or brightness at the receiver portion86In some embodiments, the first amplitude may be “on” and the second amplitude may be “off,” such that the detectors each generate a binary on-off signal in response to the alternating sequence of the pattern when the rotating member rotates. However, in other embodiments the signals could be sinusoidal, sawtooth, or have other waveforms. The first detector66generates a first signal, and the second detector70generates a second signal.

As illustrated inFIG. 4, signals from the first detector66and second detector70are received by a controller90. In the illustrated embodiment, the detectors66and70are hardwired to the controller90. In other embodiments, the first signal and/or second signal may be transmitted wirelessly to the controller. The signals received by the controller90may first be processed by a signal conditioning circuit94configured to filter or otherwise condition the raw signals from the detectors66and70. After signal conditioning, the first signal and second signal are received by a micro-processor98. The micro-processor98is configured to analyze the signals and determining the torque T. A memory module102is provided to store data, such as constants or baseline values which may be used by the micro-processor98as part of determining the applied torque T. The controller90may also receive inputs from and send outputs to additional sensors user inputs, or other user interfaces, indicated generally at106. Examples of a user interface include a keyboard and display by which an operator may enter data related to the mechanical characteristics of the shaft.

FIG. 5is a graph comparing a representative first signal110and a representative second signal114. In the illustrated embodiment, each of the first signal110and the second signal114is binary (i.e., “on” or “off”), with a square wave form. However, in other embodiments the signals could be sinusoidal, sawtooth, or have other waveforms that may require signal conditioning. It is the phase of the signals, rather than the amplitude or waveform, that is used to derive torsion and/or torque. Because the first signal110and second signal114relate to the same shaft, under steady-state conditions, and assuming that both reference members46,50and detectors66,70are identical, both signals will have the same frequency.

At any given time, the first signal110has a first phase, and the second signal114has a second phase. Comparing the first phase to the second phase with respect to the same time reference t results in a phase difference Φ. A phase difference Φ may be expressed in terms of time or in terms of degrees.

When the rotating member rotates at steady state under known load, such as at time t1, a baseline phase difference Φ0between the first signal110and second signal114is constant. The baseline phase difference Φ0may be a programmed constant value or an input determined by direct observation. Where the first reference member and second reference member have identical orientations relative to the shaft under a no load condition (i.e., zero torsion), the baseline phase difference Φ0at t1will be zero. Regardless of how or when the baseline phase difference Φ0is determined, it is later used by the controller as a comparative value for determining the applied torque T. Thus, any baseline value may be used, so long as the conditions under which it occurs are known. The baseline value is stored in memory102.

When the applied torque T is applied to the rotating member (e.g., with a dynamometer or a prime mover) at a time t2, the phase difference changes from Φ0to a loaded phase difference ΦL. Based on additional inputs including the mechanical characteristics of the rotating member, the applied torque T can be calculated by comparing the loaded phase difference ΦLto the baseline phase difference Φ0. The comparison may be expressed either as a difference or a ratio:
Φ0−ΦL=change in phase difference=ΔΦ
Φ0/ΦL=phase difference ratio

Either value may be used calculate the applied torque T since both the change in the phase difference or phase difference ratio relates to a change in torsion of the shaft. For a shaft of known mechanical characteristics, the applied torque T may be directly calculated from the torsion by well known mechanical principles. Measurement error is minimized since actual deformation, not including inertia affects, causes the change in phase difference. A speed of shaft rotation can be input from the motor that is rotating the shaft, or can be calculated based on a period of the first signal110or second signal114.

The following example illustrates one method by which the controller90may calculate an applied torque T for a shaft rotating at a known instantaneous rotational velocity measured in revolutions per minute (RPM). The amount of time for each rotational degree to pass is calculated as follows:1) Convert RPM to revolutions per second (“RPS”)
(RPM/60)=RPS2) Convert to degrees per second by multiplying by 360:
((RPM/60)*360)=Degrees per Second3) Convert to seconds per degree:
(1/((RPM/60)*360))=Seconds per Degree

The baseline phase difference Φ0is obtained by measurement or calculation. This baseline phase difference Φ0may be measured, starting at t1, by obtaining a time from an edge118of the first signal110to a corresponding edge122of the second signal114, if rotational velocity (RPM) is known. This baseline phase difference Φ0may also be calculated by recording RPM, independent of rotational velocity, as a phase shift in degrees. The phase shift value can then be used to calculate a baseline phase difference Φ0expressed in time using the known RPM of the shaft. Those of skill in the art will appreciate that shaft RPM can be determined by the controller90from either the first signal110or the second signal114.

Next, the loaded phase difference ΦLwith the unknown applied torque T is measured starting at time t2. In this example, the loaded phase difference ΦLis expressed in time rather than degrees. In this example, ΦLis the time between an edge126of the first signal110to a corresponding edge130of the second signal114.

Once ΦLand Φ0are determined, the change in the phase difference is calculated:
Φ0−ΦL=ΔΦ
Dividing the change in the phase difference ΔΦ by seconds per degree provides the change in degrees of torsion due to the applied torque:
ΔΦ/(Seconds per Degree)=Degrees of Torsion
For a shaft of known mechanical characteristics, the degrees of torsion may be used to calculate, correlate, or derive the applied torque T applied to the shaft.

FIGS. 6-9illustrate additional aspects of the invention embodied in alternative embodiments. Each of the embodiments of the invention disclosed herein shares the common principle of deriving a torque loading from the phase difference between a first signal generated by a first detector and a second signal generated by a second detector. Similar components have been given similar reference numerals, with different prefixes to distinguish the different embodiments.

FIG. 6illustrates a second embodiment of a torque measurement device238, in which a first reference member246and a second reference member250each take the form of notched or castellated disks. Solid protrusions, or teeth254, of the reference members246and250protrude outwardly radially. The teeth254are separated by radial gaps258. Each tooth254has a magnetic or electromagnetic characteristic distinguishable from the radial gaps258. Each of a first detector266and a second detector270in this embodiment includes an electromagnetic sensor, such as an inductive element, or Hall effect sensor (not shown).

A Hall effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. The Hall effect sensor may be combined with circuitry that allows the device238to act in a binary (on/off) mode. In this embodiment, signals generated by the first detector266and second detector270are similar to those illustrated inFIG. 5, and the controller90illustrated inFIG. 4is applicable to the embodiment ofFIG. 6. Where the signals are binary, the “on” signal is established when a tooth254passes by the detector266or277, and the “off” signal is established when a gap258passes by the detector266or277. This works due to a voltage difference that is created across the detector, transverse to an electric current in the detector and a magnetic field perpendicular to the detector. Polarization is reversed when a tooth254passes by the detector causing the magnetic field to reverse. The starting polarization is restored when a gap258passes by.

FIGS. 7-8illustrate a third embodiment of a torque measurement device338in which a first reference member346and a second reference member350take the form of notched or castellated disks. As with the embodiment ofFIG. 6, solid portions, or teeth354, of the disks protrude outwardly radially. The teeth are separated by radial gaps358, or “windows.”

As illustrated inFIG. 8, each detector366(or370) in this embodiment is an optical, line-of-sight detector. A light emitter378is positioned on one side of the reference member346and a light receiver386is positioned on the opposite side of the reference member. In this embodiment, an “on” signal is established when light374transmitted by the light emitter378passes through a gap358and is received at382by the light receiver386. An “off” signal is established when the light382is interrupted by a tooth354.

FIG. 9illustrates a fourth embodiment of a torque measurement device438. In this embodiment, a first reference array446and a second reference array450are substantially flush with the surface of the shaft10. The reference arrays446and450are arranged circumferentially on the shaft10at the first axial position30and the second axial position34, respectively. The reference arrays446and450include contrasting reference features454and458. Examples of the contrasting reference features include grooves, ridges, permanent magnets, alternating light reflective and non-reflective areas or other features. It should be appreciated that while multiple reference features are illustrated for each reference member, some embodiments may only have one reference feature per reference member.

The embodiment ofFIG. 9includes a first detector466and a second detector configured470to detect passage of the reference feature(s) during rotating of the shaft10. Where the reference feature has a magnetic characteristic, the corresponding first and second detectors466and470may include Hall effect sensors. Where the reference feature has optical characteristics, such as light reflective and light absorbing areas, the corresponding detectors466and470may include a light detector and light emitter, as described in the embodiment ofFIGS. 2-3.

The invention is not limited to the embodiments illustrated and described above, and is capable of being embodied in any system that includes a reference member and a detector configured to detect passage of the reference member in order to generate a signal. In all illustrated embodiments, the reference members and detectors are configured to generate a signal that corresponds to a pattern of a changing condition such as light or a magnetic field. In the optical embodiments, the detectors include a receiver and the reference members include portions that change the amount of light (e.g., permit or prevent light, or change the intensity or amount of light) that is received by the light receiver. In the magnetic embodiments, the reference members vary a magnetic field at the dectors.

Thus, the invention provides, among other things, a device and method for measuring torque in rotating machinery. Various features and advantages of the invention are set forth in the following claims.