Magnetorestrictive position sensor according to the propagation time principle having a magnetorestrictive detector unit for mechanical-elastic density waves

Abstract

Instead of tapping a mechano-elastic desnity wave (MEDW) from a wave conductor or a Villary band through a detector coil, a changing field strength H is captured by a XMR sensor which is positioned on a wave conductor or proximal to the wave conductor or on a Villary band or proximal to the Villary band.

Claims

1. A position sensor operating according to a runtime principle of a mechano-elastic density wave (MEDW), comprising: a wave conductor (3) configured as a wire; a position magnet (20) which is moveable along the wave conductor (3); and a detector assembly (105) arranged at the wave conductor (3), wherein the detector assembly (105) includes at least one XMR sensor (1) on the wave conductor, wherein said at least one XMR sensor is spaced from the wave conductor, the detector assembly further including a circuit board located between the at least one XMR sensor and the wave conductor, wherein said at least one XMR sensor is configured as a microchip and where no shielding exists between said at least one XMR sensor and said wave conductor, wherein the at least one XMR sensor is arranged so that a main plane of the at least one XMR sensor extends parallel to a longitudinally extending direction of the wave conductor, the detector assembly further including a bias magnet arranged with its pole orientation parallel to the main plane of the at least one XMR sensor and arranged so that its pole orientation is perpendicular to the longitudinally extending direction of the wave conductor, wherein the wave conductor is located on a first side of the at least one XMR sensor and the bias magnet is located on a second different side of the at least one XMR sensor that is opposite the first side.

2. A method for determining a position of said position magnet (20) of said position sensor according to claim 1 relative to said wave conductor (3) of said position sensor according to claim 1, comprising: detecting a changing magnetic induction with said at least one XMR sensor, or detecting a field strength or field orientation with said at least one XMR sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 a, b and c illustrate an arrangement of an XMR sensor directly on the wave conductor with only one XMR sensor;

(2) FIGS. 2a and b illustrate an XMR sensor at a center arm of a U shaped Villary-Band;

(3) FIG. 3 illustrates an XMR sensor directly at the wave conductor with two opposite sensors at identical longitudinal positions;

(4) FIG. 4 illustrates an XMR sensor directly at the wave conductor with two opposite sensors in various longitudinal positions;

(5) FIGS. 5a, b and c illustrate an XMR sensor in a bend of the wave conductor and/or of the Villary-Band;

(6) FIGS. 6a and b illustrate an XMR sensor between free ends of two Villery-Band at identical longitudinal positions;

(7) FIGS. 7a and b illustrate an XMR sensor between the free ends of two Villery-Bands at different longitudinal positions;

(8) FIG. 8 illustrates an XMR sensor opposite to a Villery-Band;

(9) FIG. 9 illustrates two XMR sensors protruding in identical directions and arranged opposite to one another with respect to the wave conductor;

(10) FIGS. 10a, b and c illustrate graphs showing the steps of CFD method;

(11) FIG. 11 illustrates an XMR sensor in a bridge circuit; and

(12) FIGS. 12a and b illustrate a connection of the wave conductor and the XMR sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(13) FIG. 1a initially illustrates the basic shape of a position sensor according to the run-time principal of a mechano-elastic density wave (MEDW).

(14) The wave conductor 3 extending in a straight line with a circular, typically solid cross section visible in FIG. 1c in the form of a rod or wire is configured at longitudinal position with a detector arrangement 105 for detecting a MEDW, wherein the MEDW is triggered by a position magnet 20 arranged proximal to the wave conductor 3 and influencing the wave conductor 3, wherein the position of the position magnet shall be determined as it is movable in longitudinal direction of wave conductor 20 and attached at a machine component whose position shall be detected.

(15) Thus, the detector arrangement 105 is typically disposed at one end of the wave conductor 3, wherein only a position of the wave conductor 3 is illustrated in the following figures where the detector arrangement 105 is disposed which always includes at least one MXR sensor 1 in the form of sensor chip according to the invention in the subsequent drawing figures.

(16) In FIG. 1 this plate shaped XMR sensor 1 is arranged and attached with its main plane 10 parallel to the longitudinal direction of the wave conductor 3 tangentially and laterally at the wave conductor 3, e.g. through solder joints 6 as illustrated in FIG. 1c. When the XMR sensor 1 is applied to a circuit board 7 the circuit board 7 is attached at the circumference of the wave conductor 3 with the side of the circuit board 7 that is oriented away from the sensor 1, e.g. soldered through solder joints 6, so that the sensor 1 protrudes in transversal direction to the wave conductor 3 on one side or on both sides beyond the cross-section of the wave conductor 3.

(17) Since the sensor chip 1 is typically not square but rectangular, it can be arranged with its longitudinal direction in longitudinal direction of the wave conductor 1 as illustrated in FIG. 1b or perpendicular thereto as illustrated in FIG. 1a, wherein the main measuring direction of the sensor chip 1 typically is the greater extension of its rectangular basic shape and this direction should coincide with the highest sensitivity of the sensor, preferably with the longitudinal direction of the component to be scanned, thus the wave conductor or the Villary band.

(18) When the sensor 1 is not applied to a circuit board 7 it can also be directly connected with the mechano-elastic element which shall be detected by the sensor with respect to its wave, in this case the wave conductor.

(19) In the solution according to FIG. 2a the mechano-elastic element at which the XMR sensor 1 is attached is a Villary band 4, however compared to the normal configuration of a Villary band that protrudes on one side from the wave conductor 3, this is a U-shaped Villary band 4′ which is attached in different longitudinal positions with both its free ends at the wave conductor 3, so that its connecting arm extends parallel to the longitudinal direction of the wave conductor 3.

(20) The XMR sensor 1 is applied in turn at this connecting arm on one of the large surface outsides of the Villary band 4, wherein the XMR sensor additionally includes a bias magnet 2 for reinforcing the signal, thus on a top side oriented away from the Villary band 4′ on which also contact points 5 for contacting through the signal conductors 8 for the XMR sensor 1 are disposed.

(21) FIG. 2b illustrates a solution also with an U-shaped Villary band which is attached at the wave conductor 3 with both its ends, however with the main plane of the U-shape transversal to the extension of the wave conductor 3, so that the connecting arm of the U-shape is not parallel to the wave conductor, but skewed relative to the longitudinal direction of the wave conductor 3 at which then in turn an XMR sensor 1 and possibly a bias magnet 2 are arranged, either on opposite sides of the center arm of the Villary band 4 or also built on top of one another, so that the bias magnet 2 and the Villary band 4 are arranged on opposite sides of the XMR sensor 1.

(22) Also in the solution according to FIG. 1 as illustrated in FIG. 1c a bias magnet 2 can also be arranged on the XMR sensor 1 on the opposite side of the wave conductor 3, wherein the XMR sensor 1 is then preferably positioned between the contact points 5 for the signal conductor 8 provided on the same side. The bias magnet is preferably arranged with its pole orientation parallel to the orientation of the highest sensitivity of the XMR sensor 1.

(23) FIG. 3 illustrates a solution which differs from the solution according to FIG. 1 in that two XMR sensors 1 are arranged parallel to one another on opposite sides of the cross-section of the wave conductor 3 at the wave conductor 3, wherein an additional bias magnet 2 can be arranged transversal to the main plane of the two XMR sensors 1 connecting both with its pole orientation.

(24) FIG. 4 illustrates a solution in which two XMR sensors 1 are also arranged on opposite sides of the cross-section of the wave conductor 3, but in longitudinal direction of the wave conductor 3 at two different longitudinal positions. The distance 9 of the longitudinal positions measured respectively from the center of one XMR sensor 1 to the center of the other XMR sensor 1 thus is an integer singular or multiple of the distance from wave peak to wave trough of the mechano-elastic density wave which shall be detected through the detector arrangement 105 when running along the wave conductor 3. Also here the contact points 5 with the signal conductors 8 originating therefrom are arranged on an outside of the sensor 1 respectively opposite to the wave conductor 3.

(25) FIG. 5 in turn illustrates a solution in which only one XMR sensor 1 is used for detection, however this time it is arranged in a double elbowed and thus U-shaped portion, preferably in an end portion of the wave conductor 3.

(26) The free space in the interior of the U-shape is thus sized so that in particular the XMR sensor 1 fits in there with its main plane arranged in the main plane of the U-shape, possibly with a bias magnet 2 arranged adjacent thereto or arranged there above, wherein the pole orientation of the bias magnet is preferably arranged transversal to the main extension of the wave conductor 3. Herein, like also in all other cases the XMR sensor 1 can be positioned and mounted at a small distance from the mechano-elastic element to be detected, either the wave conductor 3 itself or a Villary band 4, or so that it contacts the wave conductor 3 or a Villary band 4.

(27) In the solution according to FIG. 5b and FIG. 5c a XMR sensor 1 is also arranged in a bend of the mechano-elastic element to be monitored, however this time in the inner angle of a Villary band 4 that is bent in a single bend by 90°, wherein the Villary band is fixated at the wave conductor 3 with one of its ends as usual.

(28) The plane defined by the two arms of the Villary band 4, thus as illustrated in FIG. 5b is transversal to the longitudinal direction of the wave conductor 3 and the main plane of the XMR sensor 1 extends in parallel and preferably approximately at the level of the wave conductor 3 between the wave conductor 3 and the angled arm of the Villary band 4 further remote from the wave conductor 3.

(29) This can be achieved in that the XMR sensor 1 is mounted on a circuit board 7 which is attached with one end on the outside of the wave conductor 3 and with the other end at the angled arm of the Villary band 4. When the XMR sensor 1 is then disposed on the same side of the circuit board as the wave conductor 3 they are both approximately at the same level.

(30) Additionally a bias magnet 2 can be arranged in turn on the opposite side of the circuit board 7, preferably again with its pole orientation transversal to the longitudinal orientation of the wave conductor 3.

(31) The signal improvement thus achieved is additionally influenced in a positive manner when the same assembly is arranged proximal to a bend of the wave conductor 3 and in its interior angle as evident in FIG. 5c.

(32) FIG. 6 on the other hand illustrates a solution in which a respective Villary band 4 is attached with one of its end at the cross-section at the wave conductor 3 at the same longitudinal position on opposite sides and protrudes with the other end into the same transversal direction so that an XMR sensor 1 can be mounted between the two free ends, wherein the main plane of the XMR sensor 1 extends parallel to the longitudinal direction of the wave conductor 3, but transversal to the longitudinal directions of the Villary band 4.

(33) Since the extension of the XMR sensor 1 is greater than the cross-section of the wave conductor 3 the Villary bands 4 are preferably slightly angled or extend away from one another in a slight V-shape, thus they are not attached at the wave conductor 3 exactly opposite to one another.

(34) Since the XMR sensor 1 is attached at the Villary bands 4 only with the narrow sides of the XMR sensor, its broad sides are provided on the one hand side for receiving the contact points 5 for the signal conductors 8 and on the other side for receiving a bias magnet 2 whose pole orientation preferably extends transversal to the longitudinal axis of the wave conductor 3.

(35) FIG. 7 illustrates a solution which differs from the solution according to FIG. 6 in that the two Villary bands 4 are also arranged on opposite sides of the cross-section of the wave conductor 3 but not at the same longitudinal position but approximately offset by half the length of a bias magnet 2 which is connected analogously to FIG. 6 with the two free ends of the two Villary bands 4. Each Villary band 4 is configured with a proper XMR sensor 1 so that a redundant configuration is achieved.

(36) FIG. 8 illustrates a solution in which, differently from the solution according to FIG. 6, one Villary band 4 and one XMR sensor 1 protrude in the same direction and slightly parallel to one another from the two opposite sides of a cross-section of a wave conductor 3 instead of two Villary bands, wherein preferably a bias magnet 2 is then arranged between the freely protruding ends of the two elements, preferably in turn with its pole orientation transversal to the longitudinal direction of the main planes of the XMR sensor 1 or the Villary band 4.

(37) The solution of FIG. 9 illustrates a bias magnet 2 arranged in the same geometric assembly as in FIG. 6 instead of the two Villary bands 4 two XMR sensors 1 in turn with bias magnets 2 arranged between the free ends. The contact points 5 for the data conductors 8 are thus respectively arranged on the side of the XMR sensors 1 oriented away from the wave conductor 3.

(38) FIG. 10 illustrates another option to improve the measuring result.

(39) When only one detector assembly 105 is provided for a position sensor according to the invention, e.g. a single XMR sensor 1, which is typical, this XMR sensor 1 generates e.g. the signal S1 as illustrated in FIG. 10a.

(40) Thus, a particular signal value W0 is predetermined as a switching threshold and thus point in time of arrival of the mechano-elastic density wave at the detector assembly.

(41) Since depending on environmental impacts like temperature the amplitude and thus the flank slope of the signal S1 varies and could as well be S1′, the measuring result can vary by a time differential Δt as a function thereof which represents a measurement imprecision.

(42) The constant fraction discriminator method (CFD) which is known in principle facilitates determining an exact point in time from analog broad impulses with variable signal amplitude and variable flank slopes. This is achieved in that the amplitude level and thus the flank steepness of the signal is eliminated thus by generating a virtual second signal S2 from the output signal S1 and subsequently adding the two signals S1 and S2 to form a sum signal S3.

(43) The virtual second signal S2 as illustrated in FIG. 10b is generated from the output signal S1 in that it is moved by a fixed amount of time ΔT, in particular delayed, wherein the amount of time is smaller than the rise time of the output signal. Additionally the output signal is inverted and multiplied with a factor which is between 0 and 1.

(44) The addition yields a sum signal S3 whose zero passage with positive rise is independent from the amplitude and flank slope of the output signal S1.

(45) According to the invention instead of generating the virtual second signal S2 from the output signal S1 two real signals can be used for S1 and S2 that come from two preferably identical detector assemblies, e.g. XMR sensors offset by a defined amount in longitudinal direction, e.g. along the distance sensors.

(46) Through the offset of the detector arrangements the two signals are time offset anyhow as required for S1 and S2.

(47) In order for the amplitude of the signal arriving at the second detector assembly to be smaller than the amplitude arriving at the first detector assembly the second detector assembly also has a smaller lateral distance from the wave conductor than the first detector assembly.

(48) In order to provide the inversion and subsequent addition of the two signals S1 and S2 only the two XMR sensors have to be connected with one another accordingly, so that also a subtraction of their two signals is provided which is mathematically identical with inverting the one signal and subsequently adding both signals.

(49) This solution requires a second detector assembly, however, it avoids the computational complexity for generating the virtual second signal S2 from a real first signal S1.

(50) In particular there are numerous applications in which two detector assemblies are arranged at one wave conductor anyhow for reasons of redundancy and operational safety. As long as both detector assemblies operate correctly their signals can be directly used as signals S1 and S2 for generating the sum signal S3. Should one of the two detector assemblies fail, operations continue with the remaining functional detector assembly alone through mathematical generation of the virtual signal S2 from the real signal S1. This slightly increases processing time but the distance sensor is still fully functional.

(51) FIG. 12 illustrates a configuration with two XMR sensors 1a, 1b having the functionality recited supra.

(52) The two XMR sensors 1a and 1b and also the other electronic components for signal processing are arranged on the front sides of the circuit interconnection 7a+b provided with conductive paths, wherein the circuit interconnection includes two circuit boards 7a, b with identical circumferential contours which are connected with one another with their backsides, in particular glued together as illustrated in the frontal view of FIG. 12b.

(53) The front view of the circuit board interconnection in FIG. 12a illustrates that the circumferential contour of the particular circuit boards 7a, b is C-shaped with a bulge 15 between its freely extending arms into which the crimp sleeve 14 fits exactly through which the electric signal conductor 8 is electrically clamped onto the wave conductor 2 in its end portion.

(54) From the base of the bulge 15a longitudinal groove 12a, b extends at a backside of each of the circuit boards 7a, b at the same location so that the two non-longitudinal grooves 12a, b when glued against one another form a pass through opening for the signal conductor 8 and the wave conductor 2 extending parallel to one another starting at a sleeve 14.

(55) The attachment is preferably provided through soldering the metal crimp sleeve 14 at solder points 13c, d arranged directly adjacent thereto on the front sides of the circuit boards 7a, b.

(56) In FIG. 12a furthermore illustrates solder points 13a, b that are arranged on the front side of the illustrated circuit board 7b respectively in a square, wherein the contact points are the contact points for soldering on an XMR sensor 1a, 1b which are offset in longitudinal direction and arranged with a different distance from the wave conductor 2 on the circuit board 7a and/or 7b.

(57) As illustrated in FIG. 12b the other components of the processing electronics are also arranged on the outward oriented front sides of the circuit boards 7a, b.

(58) Since a particular XMR sensor provides a measuring result which strongly depends from environmental impacts like e.g. the current operating temperature of the distance sensor the present application preferably respectively uses a temperature compensating bridge circuit according to FIG. 11 made from a total of four XMR sensors 1a through 1d connected with one another instead of a single XMR sensor, wherein the bridge circuit can be used at any location where a single XMR sensor is recited in the instant application.

(59) Thus two respective XMR sensors 1a and 1b, or 1c, d are respectively arranged on parallel branches of an electrical circuit between grounding and a supply voltage, wherein in one case the first XMR sensor 1c and in the other case the other XMR sensor 1d are covered with a magnetic shield 11, so that they are not influenced by magnetic fields impacting them from the outside, not even by the magnetic fields of the wave conductor 2.

(60) The signal tapping is performed in both branches respectively between the two XMR sensors arranged thereon and the computation of the two tapped signals with one another yields a temperature neutral resulting signal since the non-shielded XMR sensor provides e.g. a rising particular signal in one branch and a declining particular signal in the other branch for a temperature change.

REFERENCE NUMERALS AND DESIGNATIONS

(61) 1, 1a, b XMR-Sensor, Sensorchip 1 Bias magnet 2 Wave conductor 4, 4′ Villary band 5 Contact point 6 Soldering point 7, 7a, b Circuit board 8 Signal conductor 9 Displacement 10 Main plane 11 Magnetic shielding 12a, b Longitudinal groove 13a-d Solder point 14 Crimp sleeve 15 Bulge 20 Position magnet 105 Detector assembly B Magnetic induction H Field strength Δt Time displacement