Device, arrangement and method for characterizing the torsion, rotation and/or positioning of a shaft

Abstract

The invention relates to a device, an arrangement and a method for characterizing the torsion, rotation, and/or positioning of a shaft by generating a periodic magnetic field of a magnetic field generator disposed between at least two magnetic field detectors by applying a periodic exciter signal. The field is modified by the shaft and induces an output signal at each of the magnetic field detectors. The difference with respect to amplitude or phase between the exciter signal and the first output signal is detected as a first measured variable and between the exciter signal and the second output signal is detected as a second measured variable. The total of and/or the difference between the first and the second measured variables is calculated, and the torsion, rotation, and/or positioning of the shaft is characterized based thereon.

Claims

1. A measuring device for characterizing at least one of a torsion, a rotation or a positioning of a shaft, the measuring device comprising: a first magnetic field detector and a second magnetic field detector for detecting a magnetic field; a magnetic field generator for generating a magnetic field, said magnetic field generator being disposed between said first magnetic field detector and said second magnetic field detector; the measuring device being configured to apply a chronologically periodically varying electrical exciter signal to said magnetic field generator causing said magnetic field generator to generate a chronologically periodically varying magnetic field, the magnetic field being modified by the shaft to be characterized, a first electrical output signal being induced at said first magnetic field detector and a second electrical output signal being induced at said second magnetic field detector by the modified magnetic field; the measuring device being configured to detect a difference with respect to amplitude or phase between the exciter signal and the first output signal as a first measured variable and between the exciter signal and the second output signal as a second measured variable; and the measuring device being configured to determine at least one of a sum of the first and the second measured variables or a difference between the first and the second measured variables.

2. The measuring device according to claim 1, wherein said magnetic field generator is a coil functioning as an exciter coil.

3. The measuring device according to claim 2, wherein said first magnetic field detector is a first coil functioning as a first receiver coil and said second magnetic field detector is a second coil functioning as a second receiver coil.

4. The measuring device according to claim 3, wherein said exciter coil, said first receiver coil and said second receiver coil have coil axes extending parallel to one another at a distance from one another.

5. The measuring device according to claim 1, wherein the measuring device is configured to apply at least two chronologically periodic electrical exciter signals having different frequencies to said magnetic field generator.

6. The measuring device according to claim 5, wherein the measuring device is configured to detect the first and second measured variables for each of the frequencies, to ascertain the total of the first and second measured variables for each of the frequencies, and to ascertain a torsional moment applied to the shaft based on the totals.

7. The measuring device according to claim 1, which further comprises a third magnetic field detector and a fourth magnetic field detector, said magnetic field generator being disposed between said third magnetic field detector and said fourth magnetic field detector.

8. The measuring device according to claim 7, wherein said first and second magnetic field detectors are disposed at positions along a sensor main axis, said third and fourth magnetic field detectors are disposed at positions along a sensor secondary axis, and the sensor main axis is perpendicular to the sensor secondary axis.

9. The measuring device according to claim 7, wherein: a third electrical output signal is induced at said third magnetic field detector and a fourth electrical output signal is induced at said fourth magnetic field detector by the modified magnetic field; the measuring device is configured to detect a difference with respect to amplitude or phase between the exciter signal and the third output signal as a third measured variable and between the exciter signal and the fourth output signal as a fourth measured variable; and the measuring device is configured to ascertain at least one of a total of the third and the fourth measured variables or a difference between the third and the fourth measured variables.

10. An arrangement for characterizing at least one of a torsion, a rotation or a positioning of a shaft having a shaft longitudinal axis, the arrangement comprising: a measuring device according to claim 1; said first and second magnetic field detectors being disposed with respect to a plane extending through the shaft longitudinal axis and through said magnetic field generator such that said first magnetic field detector is located on one side of the plane and said second magnetic field detector is located on the other side of the plane.

11. The arrangement according to claim 10, which further comprises: a third magnetic field detector and a fourth magnetic field detector, said magnetic field generator being disposed between said third magnetic field detector and said fourth magnetic field detector; and said third and fourth magnetic field detectors being disposed with respect to the plane extending through said magnetic field generator such that the plane extends through said third and fourth magnetic field detectors.

12. The arrangement according to claim 10, which further comprises: a third magnetic field detector and a fourth magnetic field detector, said magnetic field generator being disposed between said third magnetic field detector and said fourth magnetic field detector; said first and third magnetic field detectors being disposed on one side of the plane extending through said magnetic field generator; and said second and fourth magnetic field detectors being disposed on the other side of the plane extending through said magnetic field generator.

13. The arrangement according to claim 10, wherein a distance between said magnetic field generator and at least one of said first magnetic field detector or said second magnetic field detector is less than a diameter of the shaft to be characterized.

14. A method for characterizing at least one of a torsion, a rotation or a positioning of a shaft, the method comprising the following steps: generating a chronologically periodically varying magnetic field permeating the shaft by applying a chronologically periodically varying electrical exciter signal to a magnetic field generator, and the shaft to be characterized modifying the magnetic field; detecting a difference with respect to amplitude or phase between the exciter signal and a first electrical output signal representing a strength of the modified magnetic field at a first position as a first measured variable and between the exciter signal and a second electrical output signal representing a strength of the modified magnetic field at a second position as a second measured variable, the first and second positions not being disposed in a common radial plane (xz plane) of the shaft; and determining at least one of a sum of the first and second measured variables or a difference between the first and the second measured variables.

15. The method according to claim 14, which further comprises the following steps: detecting a difference with respect to amplitude or phase between the exciter signal and a third electrical output signal representing a strength of the modified magnetic field at a third position as a third measured variable and between the exciter signal and a fourth electrical output signal representing the strength of the modified magnetic field at a fourth position as a fourth measured variable; and ascertaining at least one of a total of the third and the fourth measured variables or a difference between the third and the fourth measured variables.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention is explained hereafter on the basis of exemplary embodiments with reference to the appended figures, wherein identical or similar features are provided with identical reference signs; in the schematic figures:

(2) FIGS. 1A, 1B show a measuring arrangement according to one embodiment having a measuring device having two magnetic field detectors,

(3) FIG. 2 shows a measuring arrangement according to a further embodiment having a measuring device having four magnetic field detectors,

(4) FIG. 3 shows a measuring arrangement according to a further embodiment having a measuring device having four magnetic field detectors, and

(5) FIG. 4 shows a top view of a cross-shaped flux conduction structure having coils.

DESCRIPTION OF THE INVENTION

(6) FIGS. 1A and 1B show a measuring arrangement 1 according to one embodiment while carrying out a measuring method according to one embodiment. The measuring arrangement 1 comprises a measuring device 3 and a shaft 5. The shaft longitudinal axis 7 coincides with the z direction of the xyz coordinate system shown in the figures. The shaft 5 at least partially consists of ferromagnetic and electrically conductive material. As an example, in the embodiment according to FIGS. 1A and 1B, the shaft 5 is a hollow shaft or solid shaft, which consists of a ferromagnetic and electrically conductive material.

(7) The measuring device 3 comprises a magnetic field generator 9, a first magnetic field detector 11, and a second magnetic field detector 13. The magnetic field generator 9 is embodied as an example as a coil, which is also referred to as an exciter coil 9. However, the magnetic field generator can also be designed in the form of another magnetic-field-generating device. The first 11 and the second 13 magnetic field detector are each embodied as a coil as an example, which are also referred to as a first receiver coil 11 and second receiver coil 13. The first and the second magnetic field detector can also be designed in the form of another magnetic-field-sensitive detector, however, for example as a Hall detector. The exciter coil 9 is arranged between the first receiver coil 11 and the second receiver coil 13.

(8) The xz plane of the xyz coordinate system shown in the figures forms a radial plane of the shaft 5. The exciter coil 9 is arranged in such a way that it is intersected by the xz plane and/or is located in the xz plane; therefore the radial plane formed by the xz plane is also referred to as the exciter radial plane. The exciter radial plane is thus spanned (together with the shaft longitudinal axis) by the x direction as the exciter plane radial direction. The exciter coil 9 is arranged in such a way that its coil axis 15 is parallel to the x axis, wherein the exciter coil axis 15 is perpendicular to the shaft longitudinal axis 7 and (in its extension) intersects the shaft longitudinal axis 7. The magnetic field (not shown) generated by the exciter coil 9 is rotationally symmetrical with respect to the exciter coil axis 15.

(9) The first receiver coil 11 is arranged on one side of the exciter radial plane (namely on the side of the xz plane having positive y values), the second receiver coil 13 is arranged on the other side of the exciter radial plane (namely on the side of the xz plane having negative y values). The first 11 and second 13 receiver coil are arranged in such a way that the receiver coil axes 17 or 19 thereof, respectively, extend in parallel to the exciter coil axis 15 (and thus in parallel to the x axis or the exciter plane radial direction), wherein the three coil axes 15, 17, 19 all extend in a plane which is parallel to the xy plane. The sensor main axis 21, which is provided by the connecting line between the first 11 and the second 13 receiver coil, extends in parallel to the y axis and perpendicular to the exciter radial plane (xz plane). An angle of 90° is thus provided between the directional vector of the shaft longitudinal axis 7 (z direction) and the directional vector of the sensor main axis 21 (y direction).

(10) The exciter coil 9 and also the first 11 and the second 13 receiver coil are formed identically to one another. The first 11 and the second 13 receiver coil are arranged equidistantly and symmetrically on both sides of the exciter coil 9 along the sensor main axis 21. The exciter coil 9 is thus arranged in the middle between the first 11 and the second 13 receiver coil.

(11) The measuring device 3 can optionally comprise a flux conduction structure 23 (not shown in FIG. 1A). According to FIG. 1B, the flux conduction structure 23 is formed E-shaped, wherein the exciter coil 9 is arranged on the middle pole of the flux conduction structure 23 and the two receiver coils 11, 13 are arranged on the two outer poles of the flux conduction structure 23. The exciter coil 9 and the receiver coils 11, 13 (and also optionally the flux conduction structure 23) form a sensor element 25 of the measuring device. During the operation of the measuring device 3, the sensor element 25 is arranged laterally adjacent to the shaft 1.

(12) The distance between the exciter coil 9 and the first receiver coil 11 is less than the diameter of the shaft 5. The distance between the exciter coil 9 and the second receiver coil 13 is also less than the diameter of the shaft 5. The internal cross section and the external cross section of each of the coils 9, 11, 13 is less than the cross section of the shaft 5. Moreover, the distance between the first receiver coil 11 and the second receiver coil 13 is less than the diameter of the shaft 5.

(13) The measuring device 3 comprises an electrical power source 27, which is connected to the exciter coil 9 and by means of which a chronologically periodically varying electrical exciter signal is applied to the exciter coil 9 during operation of the measuring device 3. As an example, the measuring device 3 is designed by means of the power source 27 for applying a harmonic alternating current of a predetermined frequency to the exciter coil 9, wherein the alternating current is used as the exciter signal. Alternatively thereto, the AC voltage accompanying the alternating current can be used as the exciter signal. A magnetic field (not shown) is generated by the exciter coil 9 due to the exciter signal, which interacts with the ferromagnetic and electrically conductive material of the shaft 5, whereby a modified overall magnetic field is generated.

(14) The modified overall magnetic field induces a voltage, which is accompanied by an electric current, in each of the receiver coils 11, 13. The measuring device 3 is designed to detect the electric current resulting at the first receiver coil 11 as a first output signal and to detect the current resulting at the second receiver coil 13 as a second output signal. Alternatively thereto, the measuring device 1 can also be designed to detect the electric voltage resulting at the first receiver coil 11 as a first output signal and to detect the voltage resulting at the second receiver coil 13 as a second output signal. The measuring device 3 comprises as an example an analysis device 29, which is connected to the first 11 and the second 13 receiver coil and is designed to detect the output signals.

(15) The analysis device 29 is connected to the electrical power source 27. The measuring device 3 is designed to detect the difference with respect to amplitude and/or phase between the exciter signal and the first output signal as a first measured variable and between the exciter signal and the second output signal as a second measured variable by means of the analysis device 29.

(16) The measuring device 3 is designed to ascertain the total of the first and the second measured variable by means of the analysis device 29. The measuring device 3 is moreover designed to ascertain the difference between the first and the second measured variable by means of the analysis device 29. Moreover, the measuring device 3 is designed to characterize the torsion state, the rotation state, and the positioning of the shaft based on the ascertained total and the ascertained difference, as explained hereafter.

(17) The first measured variable X.sub.E/R1 and the second measured variable X.sub.E/R2 can be written as follows:
X.sub.E/R1=B.sub.E−B.sub.R1=X.sub.S+X.sub.R−X.sub.T  (1)
X.sub.E/R2=B.sub.E−B.sub.R2=X.sub.S−X.sub.R−X.sub.T,  (2)

(18) wherein the index E denotes the magnetic field generator 9 (here: the exciter coil 9), the index R1 denotes the first magnetic field detector 11 (here: the first receiver coil 11), the index R2 denotes the second magnetic field detector 13 (here: the second receiver coil 13), B.sub.E denotes the reference variable of the exciter signal, B.sub.R1 denotes the reference variable of the first output signal, and B.sub.R2 denotes the reference variable of the second output signal, wherein the reference variable is either the amplitude or the phase of the respective signal.

(19) X.sub.E/R1 denotes the first measured variable, which corresponds to the difference between the reference variable of the exciter signal and the reference variable of the first output signal (i.e., the amplitude difference or the phase difference between the exciter signal and the first output signal). X.sub.E/R2 denotes the second measured variable, which corresponds to the difference between the reference variable of the exciter signal and the reference variable of the second output signal (i.e., the amplitude difference or the phase difference between the exciter signal and the second output signal). The first and second measured variable are each composed of a static contribution X.sub.S, which is dependent on the distance a between the magnetic field generator 9 and/or the sensor element 25 and the shaft 5, a contribution X.sub.R dependent on the rotational velocity of the shaft 5, and a contribution X.sub.T dependent on the torsion of the shaft 5. The required distance of the sensor element from the measurement object (shaft) is strongly dependent on the magnetic coupling between the sensor element and the measurement object (shaft) and typically moves in the range of several millimeters. A suitable measurement distance a has to be set in dependence on the magnetic conductivity of the measurement object. The smaller the measurement distance a can be selected, the better are the signal quality and dynamics, which is required for the most interference-free possible measurement signal analysis.

(20) With the present symmetrical arrangement of the first 11 and the second 13 magnetic field detector with respect to the shaft 5, the contribution X.sub.S is equal on both channels. It can thus be ensured via the contribution X.sub.S that the first 11 and the second 13 magnetic field detector (and/or the sensor element 25 of the measuring device 3) are arranged symmetrically with respect to the shaft 5.

(21) A rotation of the shaft 5 is accompanied by an increase of the detected reference variable difference by a contribution X.sub.R dependent on the rotational velocity on one of the two measurement channels and a reduction of the reference variable difference by the same contribution X.sub.R on the other of the two channels. For the case that the tangential velocity of the shaft points from the second 13 toward the first 11 magnetic field detector on the side of the shaft 5 facing toward the magnetic field generator 9 (illustrated in FIG. 1B by the arrow 31, which indicates the associated rotational direction), X.sub.R is positive, wherein the first channel or the first measured variable X.sub.E/R1 increases by the (rotational-velocity-dependent) absolute value X.sub.R and the second channel or the second measured variable X.sub.E/R2 decreases by the same absolute value X.sub.R. For the case that the tangential velocity of the shaft points from the first 11 toward the second 13 magnetic field detector (not shown) on the side of the shaft 5 facing toward the magnetic field generator 9, X.sub.R is positive, wherein the first channel or the first measured variable X.sub.E/R1 decreases by the absolute value X.sub.R and the second channel or the second measured variable X.sub.E/R2 increases by the same absolute value X.sub.R. The running direction of the shaft 5 thus determines the sign with which the contribution X.sub.R is incorporated into the first and the second measured variable, whereby the ascertainment of the running or rotational direction of the shaft 5 is enabled. The measuring device 3 can be designed, for example, in such a way that it is evaluated by it as the presence of a first rotational direction if the first measured variable is greater than the second measured variable, and it is evaluated by it as the presence of a second rotational direction if the second measured variable is greater than the first measured variable, wherein the first rotational direction is opposite to the second rotational direction.

(22) A torsion of the shaft 5, which can be provided both with resting and also with rotating shaft, is expressed in a change of the magnetization of the shaft 5 induced by the exciter magnetic field and is accompanied by an identical change of the detected reference variable difference by a contribution X.sub.T, which is dependent on the torsion, on both channels.

(23) The total ΣX.sub.12 of the first and the second measured variable results as
ΣX.sub.12=X.sub.E/R1+X.sub.E/R2=2(X.sub.S−X.sub.T),  (3)

(24) and the difference ΔX.sub.12 between the first and the second measured variable results as
ΔX.sub.12=X.sub.E/R1−X.sub.E/R2=2X.sub.R,  (4)

(25) so that, since the static contribution X.sub.S is independently ascertainable (see below), by means of calculation of the total and the difference, a separation and ascertainment of the rotational-velocity-dependent contribution X.sub.R and the torsion-dependent contribution X.sub.T is enabled. Accordingly, the contribution X.sub.R dependent on the rotational velocity can be ascertained as
X.sub.R=ΔX.sub.12/2,  (5)

(26) and the contribution X.sub.T dependent on the torsion can be ascertained as
X.sub.T=X.sub.S−ΣX.sub.12/2.  (6)

(27) The static contribution X.sub.S can be ascertained, for example, by measurement in the idle state of the shaft without rotation and without torsion of the shaft or can be set identical to zero.

(28) The contribution X.sub.R dependent on the rotational velocity v.sub.R can thus be ascertained by the measuring device 3 according to equation (5) on the basis of the difference between the first and the second measured variable, and based on the provided contribution X.sub.R, the rotational velocity v.sub.R can be ascertained, wherein v.sub.R can be provided by the tangential velocity (in the unit m/s) or the angular velocity (in the unit 1/s). At known diameter of the shaft, the tangential velocity and the angular velocity may be converted into one another without problems. The rotational velocity v.sub.R can be ascertained by the measuring device 3, for example, by a reference characteristic being stored in the measuring device which associates the associated value of the rotational velocity v.sub.R with each value of X.sub.R, for example by means of an association function v.sub.R=v.sub.R(X.sub.R), which associates an associated rotational velocity v.sub.R as a function value with a predetermined value of X.sub.R as a function argument. Such a reference characteristic or association function can be ascertained, for example, by means of a calibration, i.e., by means of targeted setting of known rotational velocities and subsequent measurement of the value of X.sub.R provided at the respective rotational velocity. During operation of the measuring device 3, a rotational velocity v.sub.R can then be associated with a detected value X.sub.R by means of comparison of the detected value X.sub.R to such a reference characteristic.

(29) Accordingly, the measuring device 3 can be designed, for example, to ascertain the difference ΔX.sub.12 between the first and the second measured variable and to ascertain the rotational velocity of the shaft 5 based on the difference.

(30) Furthermore, the contribution X.sub.T dependent on the torsion can be ascertained by the measuring device 3 according to equation (6) on the basis of the total of the first and the second measured variable (and on the basis of the known static contribution X.sub.S), and based on the provided contribution X.sub.T, for example, the torque or torsional moment M.sub.T applied to the shaft can be ascertained (in the unit Nm).

(31) The torsional moment M.sub.T can be ascertained, for example, by a reference characteristic being stored in the measuring device, which associates the associated value of the torsional moment M.sub.T with each value of X.sub.T, for example by means of an association function M.sub.T=M.sub.T(X.sub.T), which associates an associated torsional moment M.sub.T as a function value with a predetermined value of X.sub.T as a function argument. Such a reference characteristic or association function can be ascertained, for example, by means of a calibration, i.e., by means of targeted setting of known torsional moments and subsequent measurement of the value of X.sub.T provided at the respective torsional moment. During the operation of the measuring device, a torsional moment M.sub.T can then be associated with a detected value X.sub.T by means of comparison of the detected value X.sub.T with such a reference characteristic.

(32) Accordingly, the measuring device 3 can be designed, for example, to ascertain the total ΣX.sub.12 of the first and the second measured variable and to ascertain the torsion of the shaft (for example, to ascertain the torque or torsional moment applied to the shaft) based on the total.

(33) Furthermore, the measuring device can be designed to characterize the positioning of the measuring device in relation to the shaft based on the first and the second measured variable, for example to ascertain the distance between the magnetic field generator and/or sensor element and the shaft and/or to ascertain whether the first and the second magnetic field detector and/or the sensor element are arranged symmetrically with respect to the shaft.

(34) The measuring device can be designed, for example, to ascertain the first and the second measured variable in the idle state of the shaft without rotation and without torsion of the shaft. Furthermore, the measuring device can be designed in such a way that it is evaluated by it as symmetrical positioning of the first and the second magnetic field detector with respect to the shaft (and thus as correct positioning) if the first measured variable is equal to the second measured variable in the idle state of the shaft.

(35) Moreover, the measuring device 3 can be designed to ascertain X.sub.S, for example by means of a measurement in the idle state of the shaft 5 without rotation and torsion. The measuring device 3 can furthermore be designed to ascertain the distance a between the magnetic field generator 9 and/or the sensor element 25 and the shaft 5 based on the ascertained value of X.sub.S (for example, by means of comparison of an ascertained value for Xs to a corresponding reference characteristic similarly to the above procedure explained with reference to X.sub.T and X.sub.R).

(36) In that the measuring device 3 is designed to detect the first measured variable X.sub.E/R1 and the second measured variable X.sub.E/R2 and to ascertain the total ΣX.sub.12 of the first and the second measured variable and/or to ascertain the difference ΔX.sub.12 between the first and the second measured variable, therefore X.sub.R, X.sub.T, and X.sub.S can be ascertained by the measuring device 3 and inferences can be drawn therefrom about the rotation state of the shaft 5 and the positioning of the shaft 5 in relation to the sensor element 25. A conversion of the reference or contribution variables X.sub.S into a location specification (in the unit m), X.sub.T into a torsion specification (in the unit Nm), and X.sub.R into a velocity specification (unit m/s or 1/s) can be, for example, by a calibration of these variables to known measured variables such as location and/or location change, torsion, and velocity and/or by back calculation of these measured variables into the mechanical variables location (in m), torsion (in Nm), and rotational velocity (in m/s or 1/s), wherein the temperature can moreover be incorporated as a parameter.

(37) Furthermore, the measuring device 3 can be designed to ascertain the mechanical power P transmitted by the shaft according to
P=M.sub.T(X.sub.T).Math.ω(X.sub.R),  (7)

(38) wherein ω denotes the angular velocity of the shaft 5.

(39) The measuring device 3 can furthermore be designed to ascertain the efficiency n of the machine driving the shaft according to
η=P/P.sub.in,  (8)

(40) wherein P denotes the transmitted power and P.sub.in denotes the applied power.

(41) Moreover, the measuring device can be designed for the time averaging of the above-mentioned variables (in particular the detected measured variables and/or the detected total of the first and the second measured variable and/or the detected difference between the first and the second measured variable and/or the power and/or the efficiency) over a predetermined time frame, whereby chronologically smoothed measured values can be obtained.

(42) For example, by using the time-averaged measured variables X.sub.E/R1 and X.sub.E/R2 in the above equations instead of the instantaneous values X.sub.E/R1 and X.sub.E/R2, the chronological mean values of the above-mentioned parameters (for example, the chronological mean values of X.sub.S, X.sub.R, X.sub.T, P, η and the rotation parameters, location parameters, and other operation parameters computed therefrom) can be ascertained by means of the measuring device 3. The angular brackets . . . denote a chronological mean value.

(43) If the measuring device 3 is embodied as an air coil arrangement, i.e., without flux conduction structure, the measuring device can be substantially independent of thermal influences, wherein the measurement results are not subject to thermal drift.

(44) The measuring device 3 can comprise (for example, as part of the sensor element 25, see FIG. 1B) a flux conduction structure 23 for conducting the magnetic flux. An improvement of the magnetic coupling is thus enabled. Due to the improvement of the magnetic coupling between the shaft 5 and the sensor element 25, the measurement distance a of the sensor element 25 in relation to the shaft 5 can be increased, for example, because of an increase of the electrical measured variables. An increase of the electrical measured variables means an improvement of the signal-to-noise ratio (SNR) in many applications.

(45) The measurement results supplied by the measuring device 3 can be subject to a thermal drift, which can result in a corruption of the measurement results ascertained by the measuring device 3 (for example, in the event of varying ambient temperature). Such a thermal drift can be caused, for example, by the temperature dependence of the material properties of the flux conduction structure 23 and/or the shaft 5. The introduction of a high-permeability flux conduction structure 23 can thus influence the above-explained measuring method in such a way that a thermal drift is overlaid on the electrical measured variables X.sub.E/R1 and X.sub.E/R2, which can subsequently be isolated and compensated for to improve the measurement accuracy. This temperature dependence can be taken into consideration by means of a temperature-dependent correction parameter X.sub.θ (wherein θ denotes the temperature), wherein equations (1) and (2) assume the following form:
X.sub.E/R1=B.sub.E−B.sub.R1=X.sub.S+X.sub.R−X.sub.T−X.sub.θ  (9)
X.sub.E/R2=B.sub.E−B.sub.R2=X.sub.S−X.sub.R−X.sub.T−X.sub.θ.  (10)

(46) In this case, the total ΣX.sub.12 of the first and the second measured variable results as
ΣX.sub.12=X.sub.E/R1+X.sub.E/R2=2(X.sub.S−X.sub.T−X.sub.θ),  (11)

(47) and the difference ΔX.sub.12 between the first and the second measured variable furthermore results as
ΔX.sub.12=X.sub.E/R1−X.sub.E/R2=2X.sub.R,  (12)

(48) so that the rotation-dependent contribution X.sub.R can be ascertained as usual as
X.sub.R=ΔX.sub.12/2,  (13)

(49) while in contrast the torsion-dependent contribution X.sub.T results from
X.sub.T=X.sub.S−X.sub.θ−ΣX.sub.12/2.  (14)

(50) The velocity-proportional fraction X.sub.R of the amplitude or phase change can again be ascertained directly. The torsion-proportional signal fraction X.sub.T is overlaid by a drift-proportional signal fraction X.sub.θ in addition to the fraction X.sub.S presumed as known.

(51) In this regard, it can be provided that the measuring device 3 comprises a temperature sensor 33 and is designed to ascertain the value of the temperature-dependent correction parameter X.sub.θ based on the temperature detected by the temperature sensor 33. The measuring device 3 can moreover be designed to ascertain the contribution X.sub.T dependent on the torsion according to equation (14) on the basis of the total ΣX.sub.12 of the first and the second measured variable in consideration of the ascertained value for X.sub.θ, wherein based on the provided contribution X.sub.T, for example, the torsional moment M.sub.T applied to the shaft can be ascertained (in the unit Nm).

(52) The values of X.sub.θ for different temperatures θ can be ascertained, for example, by means of a calibration, i.e., by means of targeted setting of known temperatures and subsequent ascertainment of the value of X.sub.θ provided at the respective temperature and stored as a reference characteristic in the measuring device 3. According to FIG. 1B, the temperature sensor 33 is arranged as an example in contact with the flux conduction structure 23, so that the temperature of the flux conduction structure 23 is detected by the temperature sensor 33.

(53) Instead of the instantaneous values X.sub.E/R1 and X.sub.E/R2, the chronologically averaged measured variables X.sub.E/R1 and X.sub.E/R2 can also be used in above equations (13) and (14) to ascertain chronologically averaged measurement results.

(54) Alternatively to the correction of the thermally-related drift by means of measurement of the temperature, it can be provided that the measuring device 3 (for example, by designing and activating the power source 27 accordingly) is designed to apply at least two different excitation frequencies to the exciter coil 9 and analyze the measured variables provided for the different excitation frequencies. It can be provided, for example, that the measuring device 3 is designed to detect the total ΣX.sub.12 for each of the excitation frequencies and to ascertain the torsion-dependent contribution X.sub.T based on the ascertained totals.

(55) As an example, the measuring device 3 can be designed for the (simultaneous or sequential) application of a first exciter signal having a first frequency Ω.sub.1 and of a second exciter signal having a second frequency Ω.sub.2 to the exciter coil 9. The total of the first measured variable and the second measured variable is then provided for the two excitation frequencies Ω.sub.1, Ω.sub.2:
X.sub.S−X.sub.T−X.sub.θ.sub.Ω.sub.1=½ΣX.sub.E/R1+X.sub.E/R2.sub.Ω.sub.1=½ΣX.sub.12.sub.Ω.sub.1  (15)
X.sub.S−X.sub.T−X.sub.θ.sub.Ω.sub.2=½ΣX.sub.E/R1+X.sub.E/R2.sub.Ω.sub.2=½ΣX.sub.12.sub.Ω.sub.2.  (16)

(56) With a system-invariant transfer function G(Ω.sub.1,Ω.sub.2), which may be ascertained by computer or experimentally for the measuring arrangement, this linear equation system may be solved for X.sub.θ with the assumption of X.sub.Stat.=0 or X.sub.Stat ≠0 and thus a possible thermal drift may be compensated for. By means of this frequency-based compensation method, in addition to measured variable changes which originate from temperature changes of the flux conduction structure 23, measured variable changes which originate from temperature changes of the shaft 5 may also be compensated for.

(57) Alternatively to the correction of the thermal drift, it can also be provided that such a drift is prevented and/or limited beforehand, for example by means of regulation of the temperature (thermostatic control) of the measuring device 3 and/or of the sensor element 25 or of parts thereof. In this regard, it can be provided that the measuring device 3 comprises a temperature control device (not shown) for the temperature control of the flux conduction structure to a predetermined constant temperature. In the device analogous to FIGS. 1A and 1B, an analysis by means of vector voltmeter can also be provided (not shown), as briefly described hereafter. In this case, the activation signal is generated via microcontroller. The signal generation is performed by a “signal genesis” via “lookup table”, in which the chronological (phase, frequency) and amplitude-faithful value specification of the signal is variably predetermined. The value specification which discretely specifies the chronological and amplitude-faithful signal form is converted via a “direct digital synthesis” into a discrete electric signal. A “digital-to-analog converter” associates the weighted amplitudes at the corresponding time step with a voltage value and thus forms an analog signal available at the output of the D-A converter. This analog signal is amplified as desired by an amplifier in the circuit of a constant current source. The transmitter inductance LE supplied by the amplifier generates a magnetic field, which is modulated in dependence on torsion and angular velocity, etc. The magnetic induction of the transmitter coil modulated by the measurement object is converted by the receiver coils LR into an analog electric signal (D-A conversion). The analog-digital conversion is performed by the corresponding converter. The downstream phase comparators analyze the “random” position of the phase indicator. The phase indicator of the reference channel is shifted by 90°, that of the measurement channel is readjusted variably to a phase of 90° in relation to the reference to obtain an orthogonal system of the measurement voltages. If this orthogonal system becomes misaligned by the measurement effect due to an effect-related phase shift, this can be computed from the integrated voltages Ux and/or Uy.

(58) FIG. 2 shows a measuring arrangement 1 having a measuring device 3 according to another embodiment. In addition to the elements explained with reference to FIGS. 1A and 1B, the measuring device 3 according to FIG. 2 comprises a third magnetic field detector 35 and a fourth magnetic field detector 37. In FIG. 2, the power source 27, the analysis device 29, and the optional flux conduction structure 23 are not shown for better comprehensibility. As an example, in the embodiment according to FIG. 2, the shaft 5 is a hollow shaft or solid shaft which consists of a ferromagnetic and electrically conductive material.

(59) The third 35 and the fourth 37 magnetic field detector are each embodied as a coil as an example, which are also denoted as a third receiver coil 35 and a fourth receiver coil 37. The third and the fourth magnetic field detector can also be designed in the form of another magnetic-field-sensitive detector, however, for example as a Hall detector. The exciter coil 9 is arranged between the third receiver coil 35 and the fourth receiver coil 37.

(60) According to FIG. 2, the third receiver coil 35 and the fourth receiver coil 37 are arranged in such a way that they are intersected by the exciter radial plane (xz plane) and/or are located in the exciter radial plane. The third 35 and fourth 37 receiver coil are arranged in such a way that the receiver coil axes 39 and 41 thereof, respectively, extend in parallel to the exciter coil axis 15 (and thus in parallel to the x axis and/or the exciter plane radial direction). The coil axes 17, 19, 39, 41 of all four receiver coils 11, 13, 35, 37 thus also extend in parallel to one another. The sensor secondary axis 43, which is provided by the connecting line between the third 35 and the fourth 37 receiver coil, extends in parallel to the z axis according to FIG. 2. The sensor secondary axis 43 thus extends perpendicularly to the sensor main axis 21. Moreover, both the exciter coil axis 15 and also the receiver coil axes 17, 19, 39, 41 extend perpendicularly to the sensor secondary axis 43. According to FIG. 2, the sensor main axis 21 thus extends perpendicularly to the exciter radial plane (xz plane), while in contrast the sensor secondary axis 23 is located within the exciter radial plane.

(61) The third 35 and the fourth 37 receiver coil are formed identically to one another and identically to the other coils 9, 11, 13. The third 35 and the fourth 37 receiver coil are arranged equidistantly and symmetrically on both sides of the exciter coil 9 along the sensor secondary axis 43. The exciter coil 9 is thus arranged in the middle between the third 35 and the fourth 37 receiver coil. Moreover, all four receiver coils 11, 13, 35, 37 are arranged equidistantly from the exciter coil 9. In the embodiment according to FIG. 2, the four receiver coils are thus arranged in a cross shape and at equidistant intervals around the exciter coil.

(62) The measuring device 3 according to FIG. 2 can optionally comprise a cross-shaped flux conduction structure having five poles according to FIG. 4 (not shown in FIG. 2), wherein the exciter coil 9 is arranged on the central pole 45 and each of the receiver coils 11, 13, 35, 37 is arranged on one of the peripheral poles 47, 49, 51, 53 of the cross-shaped flux conduction structure 23.

(63) The distance between the exciter coil 9 and the third receiver coil 35 is less than the diameter of the shaft 5. The distance between the exciter coil 9 and the fourth receiver coil 37 is also less than the diameter of the shaft 5. The internal cross section and the external cross section of each of the coils 9, 11, 13, 35, 37 is less than the cross section of the shaft 5. Moreover, the distance between the third receiver coil 35 and the fourth receiver coil 37 is less than the diameter of the shaft 5.

(64) The modified overall magnetic field also induces a voltage in the third 35 and the fourth 37 receiver coil which is accompanied by an electric current. The analysis device 29 is also connected to the third 35 and the fourth 37 receiver coil (not shown). The measuring device 3 is designed to detect the electric current resulting at the third receiver coil 35 as a third output signal and to detect the current resulting at the fourth receiver coil 37 as a fourth output signal by means of the analysis device 29. Alternatively thereto, the measuring device 3 can also be designed to detect the electric voltage resulting at the third receiver coil 35 as a third output signal and to detect the voltage resulting at the fourth receiver coil 37 as a fourth output signal. The measuring device 3 according to FIG. 2 is designed analogously to the embodiment according to FIGS. 1A, 1B to ascertain the first measured variable X.sub.E/R1 as a first measurement channel, to ascertain the second measured variable X.sub.E/R2 as a second measurement channel, to ascertain the total ΣX.sub.12 of the first and the second measured variable, and to ascertain the difference ΔX.sub.12 between the first and the second measured variable.

(65) In the embodiment according to FIG. 2, the measuring device 3 (in addition to the functionality described with reference to FIG. 1) is moreover designed to detect the difference with respect to amplitude and/or phase between the exciter signal and the third output signal as the third measured variable and between the exciter signal and the fourth output signal as the fourth measured variable by means of the analysis device 29.

(66) In the embodiment according to FIG. 2, the measuring device 3 (in addition to the functionality described with reference to FIG. 1) is moreover designed to ascertain the total of the third and the fourth measured variable by means of the analysis device 29. The measuring device 3 is moreover designed to ascertain the difference between the third and the fourth measured variable by means of the analysis device 29. Moreover, the measuring device 3 is designed to characterize the torsion state, the rotation state, and the positioning of the shaft based on the ascertained total and the ascertained difference, as explained hereafter.

(67) The third measured variable X.sub.E/R3 and the fourth measured variable X.sub.E/R4 can be written as follows:
X.sub.E/R3=B.sub.E−B.sub.R3  (17)
X.sub.E/R4=B.sub.E−B.sub.R4,  (18)

(68) wherein the index E denotes the magnetic field generator 9 (here: the exciter coil 9), the index R3 denotes the third magnetic field detector 35 (here: the third receiver coil 35), the index R4 denotes the fourth magnetic field detector 37 (here: the fourth receiver coil 37), B.sub.E denotes the reference variable of the exciter signal, B.sub.R3 denotes the reference variable of the third output signal, and B.sub.R4 denotes the reference variable of the fourth output signal, wherein the reference variable is either the amplitude or the phase of the respective signal.

(69) For the measuring arrangement according to FIG. 2, the total ΣX.sub.34 of the third measured variable X.sub.E/R3 and the fourth measured variable X.sub.E/R4 results as
ΣX.sub.34=X.sub.E/R3+X.sub.E/R4=2(X.sub.S−X.sub.T),  (19)

(70) wherein the embodiment according to FIG. 2 is designed as an example to detect the total ΣX.sub.34 as a third measurement channel. Therefore, two equations for the two unknowns X.sub.S and X.sub.T are provided by equations (3) and (19), so that both X.sub.T and also X.sub.S can be ascertained. Accordingly, a calibration of X.sub.S can be omitted.

(71) Therefore, in the embodiment according to FIG. 2, the measuring device can be designed, for example, to ascertain X.sub.S based on the total ΣX.sub.12 of the first and the second measured variable and on the total ΣX.sub.34 of the third and the fourth measured variable. Moreover, the measuring device 3 can be designed to ascertain the distance a between the sensor element 25 and the shaft 5 based on the ascertained value for X.sub.S.

(72) If the measuring device 3 according to FIG. 2 is embodied as an air coil arrangement, i.e., without flux conduction structure, the measuring device can be substantially independent of thermal influences and/or drift-free, wherein the measurement results are not subject to thermal drift. However, the measurement results supplied by the measuring device 3 according to FIG. 2 can also be subject to a thermal drift, wherein such a thermal drift can be caused, for example, by the temperature dependence of the material properties of the cross-shaped flux conduction structure 23 and/or the shaft 5. This thermal drift can be corrected or prevented, for example, similarly to the procedures described with reference to the embodiment according to FIGS. 1A and 1B. If the measuring device 3 is embodied having a temperature sensor and compensation of the thermal drift by means of a correction factor, which is ascertained in dependence on the temperature ascertained by means of the temperature sensor, the number of the required measurement channels can be left at three. The number of the required measurement channels can also be left at three if a thermal drift is prevented by means of thermostatic control by a temperature control unit. If the thermal drift is compensated for by means of use of exciter signals having different frequencies, a fourth measurement channel can be required.

(73) Otherwise, the construction and the functionality of the measuring arrangement according to FIG. 2 correspond to those of the measuring arrangement according to FIGS. 1A, 1B, so that reference is made in this regard to the explanations with reference to FIGS. 1A and 1B.

(74) FIG. 3 shows a measuring arrangement 1 according to another embodiment, wherein the coil arrangement having the exciter coil 9 and the four receiver coils 11, 13, 35, 37 is rotated mathematically positively by 45° in relation to the embodiment according to FIG. 2, specifically around the exciter coil axis 15 as the axis of rotation. The power source 27, the analysis device 29, and the optional flux conduction structure 23 are also not shown in FIG. 3 for better comprehensibility. According to FIG. 3, the first receiver coil 11 and the third receiver coil 35 are arranged on one side of the exciter radial plane provided by the xz plane (namely on the side of the xz plane having positive y values), wherein the second receiver coil 13 and the fourth receiver coil 37 are arranged on the other side of the exciter radial plane (namely on the side of the xz plane having negative y values). In the embodiment according to FIG. 3, the sensor main axis 21 thus forms an angle of 45° with the exciter radial plane, wherein moreover the sensor secondary axis 43 also forms an angle of 45° with the exciter radial plane, wherein the sensor secondary axis 43 extends perpendicularly to the sensor main axis 21 analogously to FIG. 2.

(75) The embodiment of the measuring arrangement and the measuring method according to FIG. 3 are suitable in particular for shafts 5, which comprise a coating having ferromagnetic and electrically conductive material on the outer circumference thereof (wherein the remainder of the shaft can consist of non-ferromagnetic material). As an example, in the embodiment according to FIG. 3, the shaft 5 is a hollow shaft or solid shaft made of a non-ferromagnetic material, which is coated on its external circumference using a layer made of a ferromagnetic and electrically conductive material.

(76) For the geometry of the measuring arrangement 1 according to FIG. 3, the first, second, third, and fourth measured variable can then be written as follows:
X.sub.E/R1=X.sub.S+X.sub.R+X.sub.T  (20)
X.sub.E/R2=X.sub.S−X.sub.R+X.sub.T  (21)
X.sub.E/R3=X.sub.S+X.sub.R−X.sub.T  (22)
X.sub.E/R4=X.sub.S−X.sub.R−X.sub.T,  (23) since a (homogeneous) ferromagnetic coating of the shaft is loaded with tension along a first direction (also denoted as tension direction) and is loaded with compression along a second direction (also denoted as compression direction) when a torsional moment is applied to the shaft 5 and a torsion of the shaft is thus provided. This is accompanied by an increase of the magnetic susceptibility in the tension direction and a reduction of the magnetic susceptibility in the compression direction. For the case that the tension direction of the shaft load in the case of torsion extends along the sensor main axis 21 and the compression direction extends along the sensor secondary axis 43, X.sub.T is positive, wherein the first measured variable X.sub.E/R1 and the second measured variable X.sub.E/R2 increase by the (torsion-dependent) absolute value X.sub.T and wherein the third measured variable X.sub.E/R3 and the fourth measured variable X.sub.E/R4 decrease by the same absolute value X.sub.T.

(77) The contributions X.sub.S, X.sub.R, and X.sub.T can be separated from one another and ascertained by corresponding calculation of the total and the difference from equations (20) to (23). Since three variables are to be ascertained with X.sub.S, X.sub.R, and X.sub.T, a three-channel measurement is required. If the static contribution X.sub.S is known (for example, from a separate measurement without rotation and torsion of the shaft 5), a two-channel measurement is sufficient.

(78) If the measuring device 3 according to FIG. 3 is embodied as an air coil arrangement, i.e., without flux conduction structure, the measuring device can be substantially independent of thermal influences and/or drift-free, wherein the measurement results are not subject to a thermal drift. However, the measurement results supplied by the measuring device 3 according to FIG. 3 can also be subject to a thermal drift, wherein such a thermal drift can be caused, for example, by the temperature dependence of the material properties of the cross-shaped flux conduction structure 23 and/or the shaft 5.

(79) This temperature dependence can be taken into consideration by means of a temperature-dependent correction parameter X.sub.θ (wherein θ denotes the temperature), whereby equations (20) to (21) assume the following form in consideration of the temperature-dependent correction parameter X.sub.θ:
X.sub.E/R1=X.sub.S+X.sub.R+X.sub.T−X.sub.θ  (24)
X.sub.E/R2=X.sub.S−X.sub.R+X.sub.T−X.sub.θ  (24)
X.sub.E/R3=X.sub.S+X.sub.R−X.sub.T−X.sub.θ  (26)
X.sub.E/R4=X.sub.S−X.sub.R−X.sub.T−X.sub.θ.  (27)

(80) The parameter space is thus increased (for example, upon use of a magnetic flux conduction structure because of the temperature dependence of its material properties) by the variable X.sub.θ, which has to be separated from the variables X.sub.S, X.sub.R, and X.sub.T.

(81) This thermal drift can be corrected or prevented, for example, similarly to the procedures described with reference to the embodiment according to FIGS. 1A, 1B, and 2. Since four variables are to be ascertained with X.sub.S, X.sub.R, X.sub.T, and X.sub.θ, a four-channel measurement is required. If the static contribution X.sub.S is known (for example, from a separate measurement without rotation and torsion of the shaft 5), a three-channel measurement is sufficient. If the measuring device 3 according to FIG. 3 is embodied having a temperature sensor and compensation of the thermal drift by means of a correction factor, which is ascertained in dependence on the temperature ascertained by means of the temperature sensor, the number of the required measurement channels can also be reduced by one channel. The number of the required measurement channels can also be reduced by one channel in the case of prevention of a thermal drift by means of thermostatic control by a temperature control unit. In the case of compensation of the thermal drift by means of use of exciter signals having different frequencies, four measurement channels can be required.

(82) For the case, in the arrangement according to FIG. 3, that the shaft 5 is a hollow shaft or solid shaft made of a non-ferromagnetic material, which is coated on its outer circumference using a layer made of a ferromagnetic and electrically conductive material (also referred to as a laminated shaft), in principle only three coils (including the transmitter coil) are required for the detection of velocity, torsion, and location in comparison to the linear coil arrangement. A measurement of the mentioned parameters can thus be performed via half of the arrangement. The fundamental relationships result as follows:
X.sub.E/R1=X.sub.S+X.sub.R+X.sub.T  (28)
X.sub.E/R2=X.sub.S−X.sub.R+X.sub.T  (29)
X.sub.E/R3=X.sub.S+X.sub.R−X.sub.T  (30)
X.sub.E/R4=X.sub.S−X.sub.R−X.sub.T.  (31)

(83) It follows from the totals of the equations associated in pairs from equations (28) to (31):
ΣX.sub.14=ΣX.sub.32=2X.sub.S  (32)

(84) and it follows from the differences:
ΔX.sub.14=2(X.sub.R+X.sub.T)  (33)
ΔX.sub.32=2(X.sub.R−X.sub.T).  (34) Since the reduction of the signal in the compression direction corresponds to the increase in the tension direction, the two differences ΔX.sub.14 and ΔX.sub.32 are comparable or equivalent.

(85) The arrangement according to FIG. 3 can also be used for non-laminated measurement objects (shaft without functional layer), for example for solid or hollow shafts consisting completely of ferromagnetic and electrically conductive material. In this case, in principle only three coils (including the exciter coil) are required for the detection of velocity, torsion, and location in comparison to the linear coil arrangement. A measurement of the mentioned parameters can thus be performed via half of the arrangement. The fundamental relationships result as follows:
X.sub.E/R1=X.sub.S+X.sub.R−X.sub.T  (35)
X.sub.E/R4=X.sub.S−X.sub.R−X.sub.T  (36)
or alternately
X.sub.E/R3=X.sub.S+X.sub.R−X.sub.T  (37)
X.sub.E/R2=X.sub.S−X.sub.R−X.sub.T.  (38)

(86) In turn it follows from the total of the equations associated in pairs from equations (35) to (38):
ΣX.sub.14=ΣX.sub.32=2(X.sub.S−X.sub.T)  (39)
and from the difference:
ΔX.sub.14=ΔX.sub.32=2X.sub.R.  (39)

LIST OF THE REFERENCE SIGNS USED

(87) 1 measuring arrangement 3 measuring device 5 shaft 7 shaft longitudinal axis 9 magnetic field generator/exciter coil 11 first magnetic field detector/first receiver coil 13 second magnetic field detector/second receiver coil 15 coil axis of the exciter coil/exciter coil axis 17 coil axis of the first receiver coil 19 coil axis of the second receiver coil 21 sensor main axis 23 flux conduction structure 25 sensor element 27 electrical power source 29 analysis device 31 rotational direction of the shaft 33 temperature sensor 35 third magnetic field detector/third receiver coil 37 fourth magnetic field detector/fourth receiver coil 39 coil axis of the third receiver coil 41 coil axis of the fourth receiver coil 43 sensor secondary axis 45-53 poles of the cross-shaped flux conduction structure a distance between sensor element and shaft X.sub.E/R1 first measured variable X.sub.E/R2 second measured variable X.sub.E/R3 third measured variable X.sub.E/R4 fourth measured variable ΣX.sub.nm total of the nth and the mth measured variable ΔX.sub.nm difference between the nth and the mth measured variable