INDUCTIVE POSITION SENSOR COMPRISING AT LEAST ONE TRANSMIT COIL, AN ABSOLUTE POSITION RECEIVE COIL PAIR, A HIGH-RESOLUTION POSITION RECEIVE COIL PAIR AND A CONDUCTIVE MOVING TARGET

Abstract

An inductive position sensor including at least one transmit coil, an absolute position receive coil pair, a high-resolution position receive coil pair and a conductive moving target, the absolute position receive coil pair and the high-resolution receive coil pair together define a measurement area of the inductive position sensor and the moving target can move in this measurement area, the absolute position coil pair has a first sine receive coil and a first cosine receive coil, both having one period over the measurement area of the inductive position sensor, the high-resolution position receive coil pair has a second sine receive coil and a second cosine receive coil, both having at least two periods over the measurement area of the inductive position sensor, the absolute position receive coil pair and the high-resolution position receive coil pair are arranged in the same area of a printed-circuit board of the inductive position sensor.

Claims

1. An inductive position sensor comprising: at least one transmit coil, an absolute position receive coil pair, a high-resolution position receive coil pair and a conductive moving target, wherein the absolute position receive coil pair and the high-resolution receive coil pair together define a measurement area of the inductive position sensor and the moving target can move in this measurement area, wherein the absolute position coil pair has a first sine receive coil and a first cosine receive coil, both having one period over the measurement area of the inductive position sensor, wherein the high-resolution position receive coil pair has a second sine receive coil and a second cosine receive coil, both having at least two periods over the measurement area of the inductive position sensor, and wherein the absolute position receive coil pair and the high-resolution position receive coil pair are arranged in the same area of a printed-circuit board of the inductive position sensor.

2. The inductive position sensor according to claim 1, wherein the inductive position sensor is a radial position sensor and the measurement area is a 360° circle.

3. The inductive position sensor according to claim 1, wherein the inductive position sensor is a linear position sensor and the measurement area is a straight line.

4. The inductive position sensor according to claim 1, further comprising a signal processing unit, for providing a signal to the at least one transmit coil and/or for processing the signals of the absolute position receive coil pair and the high-resolution receive coil pair.

5. The inductive position sensor according to claim 4, wherein the signal processing unit is arranged on the same printed-circuit board as the inductive position sensor or externally connected to the printed-circuit board of the inductive position sensor.

6. The inductive position sensor according to claim 1, wherein the conductive moving target comprises multiple sections spaced apart from each other.

7. The inductive position sensor according to claim 6, wherein the multiple sections of the conductive moving target have the same shape and/or spacing.

8. The inductive position sensor according to claim 1, wherein the conductive moving target comprises at least one first target element and at least one second target element, wherein the shape of the at least one first target element is different to the shape of the at least one second target element.

9. The inductive position sensor according to claim 8, wherein the multiple sections of the at least one first target element covers the complete measurement area of the inductive position sensor or the measurement area of the inductive position sensor not covered by the at least one second target element.

10. The inductive position sensor according to claim 8, wherein the at least one second target element covers a part of the measurement area of the inductive position sensor.

11. The inductive position sensor according to claim 10, wherein the at least one second target element has a semi-circular shape, an arc segment of a full ring shape, a rectangular shape or an arrow shape.

12. The inductive position sensor according to claim 8, wherein the at least one first target element and the at least one second target element are arranged next to each other or are at least partially overlapping each other.

13. The inductive position sensor according to claim 12, wherein the at least one first target element and the at least one second target element are totally overlapping but having different sizes.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS In the following the invention will be further explained with respect to the embodiments shown in the attached figures. It shows:

[0038] FIG. 1 a schematic view of a first embodiment of an inductive position sensor according to the invention;

[0039] FIG. 2 a schematic view of a second embodiment of an inductive position sensor according to the invention;

[0040] FIG. 3 a first embodiment of a conductive moving target;

[0041] FIG. 4 a second embodiment of a conductive moving target;

[0042] FIG. 5 a third embodiment of a conductive moving target;

[0043] FIG. 6 a fourth embodiment of a conductive moving target;

[0044] FIG. 7 a fifth embodiment of a conductive moving target;

[0045] FIG. 8 a sixth embodiment of a conductive moving target;

[0046] FIGS. 9a, 9b performance comparisons for different embodiments of the conductive moving target;

[0047] FIG. 10 outputs of an inductive position sensor according to the invention after signal processing; and

[0048] FIG. 11 a schematic view of a third embodiment of an inductive position sensor according to the invention.

DETAILED DESCRIPTION

[0049] FIG. 1 shows a schematic view of a first embodiment of an inductive position sensor 1 according to the invention. The inductive position sensor 1 comprises a transmit coil 2, an absolute position receive coil pair 3, 4, a high-resolution receive coil pair 5,6 and a conductive moving target 7. The absolute position receive coil pair 3, 4 and the high-resolution receive coil pair 5, 6 together define a measurement area of the inductive position sensor 1 and the moving target 7 can move in this measurement area. The first embodiment shown in FIG. 1 refers to a radial inductive position sensor 1 and the measurement area is a 360° circle.

[0050] The absolute position coil pair 3, 4 has a first sine receive coil 3 and a first cosine receive coil 4, both 3, 4 having one period over the measurement area of the inductive position sensor 1. The high-resolution position receive coil pair 5, 6 has a second sine receive coil 5 and a second cosine receive coil 6, both 5, 6 having at least two periods over the measurement area of the inductive position sensor 1. According to the embodiment shown in FIG. 1 the second sine receive coil 5 and a second cosine receive coil 6 each have 8-periods over the measurement area.

[0051] According to the present invention the absolute position receive coil pair 3, 4 and the high-resolution position receive coil pair 5, 6 are arranged in the same area of a printed-circuit board 8 of the inductive position sensor 1.

[0052] The inductive position sensor 1 shown in FIG. 1 further comprises a signal processing unit 9, for providing a signal to the at least one transmit coil 2 and for processing the signals of the absolute position receive coil pair 3, 4 and the high-resolution receive coil pair 5, 6. According to the embodiment shown in FIG. 1 the signal processing unit 9 is externally connected to the printed-circuit board 8 of the inductive position sensor 1. In an alternative embodiment of the invention the signal processing unit 9 is arranged on the same printed-circuit board 8 as the inductive position sensor 1. The connections between the signal processing unit 9 and the transmit coil 2, the absolute position receive coil pair 3, 4 and the high-resolution receive coil pair 5, 6 have been numbered identically to the respective coil. During use of the inductive position sensor 1 shown in FIG. 1 the signal processing unit 9 provides an excitation current to the transmit coil 2, which creates an electro-magnetic field due to the excitation current. The conductive moving target 7 is located inside this created electro-magnetic field of the transmit coil 2 and therefore modifies the electro-magnetic field due to eddy currents induced into the conductive moving target 7. The absolute position receive coil pair 3, 4 and the high-resolution receive coil pair 5, 6 can sense the modifications in the electro-magnetic field due to the conductive moving target 7 and the position of the conductive moving target 7. The signals of the absolute position receive coil pair 3, 4 and the high-resolution receive coil pair 5, 6 are used by the signal processing unit 9 to determine the absolute position and the high-resolution position of the conductive moving target 7 in the measurement area.

[0053] FIG. 2 shows a schematic view of a second embodiment of an inductive position sensor 1 according to the invention. The second embodiment shown in FIG. 2 differs from the first embodiment shown in FIG. 1 in that the inductive position sensor comprises two transmit coils 2 and in that the second sine receive coil 5 and a second cosine receive coil 6 each have 32-periods over the measurement area. Otherwise, the second embodiment corresponds to the first embodiment.

[0054] The implementation of a high-resolution absolute sensor 1 with a 32-periodic receive coil pair 5, 6, an absolute 1×360 deg receive coil pair 3,4, two separate transmitter coils 2 and a signal processing unit 9 with two inductive position sensor ICs (not shown) with a 12 bit signal acquisition the theoretic resolution is 32×12 bit which is 131072 counts or 17 bit.

[0055] It is known that the sensor linearity will be lower depending on system configuration and tolerances.

[0056] The implementation of the high-resolution absolute sensor 1 with a 32-periodic receive coil pair 5, 6, a 1×360 absolute receive coil pair 3,4 and one shared signal processing unit 9 is shown in FIG. 2.

[0057] Generally the target must be designed to generate signal for both high-resolution receive coil pair 5, 6 and absolute position receive coil pair 3, 4. The accuracy and robustness over tolerances will depend on the target configuration. Below are some implementation examples. FIG. 3 shows a first embodiment of a conductive moving target 7. The conductive moving target 7 comprises multiple sections 12 spaced apart from each other. The multiple sections 12 of the conductive moving target 7 have the same shape and spacing. One or more portions of the incremental n-period sensor target 7 are removed to generate sufficient signal on the 1-periodic absolute position receive coil pair 3, 4.

[0058] FIG. 4 shows a second embodiment of a conductive moving target 7. FIG. 4 shows the upper and lower side of a substrate, wherein one side comprises a first target element 10 and the other side comprises a second target element 11, wherein the shape of the first target element 10 is different to the shape of the at least one second target element 11. Particularly, the first target element 10 comprises multiple sections 12, spaced apart from each other. The multiple sections 12 of the conductive moving target 7 have the same shape and spacing and cover the complete circumference of the circular substrate building the conductive moving target 7. Thus, the multiple sections 12 of the first target element 10 cover the complete measurement area of the inductive position sensor 1. The second target element 11 has a semi-circular shape and overs a half-circle of the circular substrate of the conductive moving target 7. The first element 10 and second element 11 of the conductive moving target 7 overlap with each other, as FIG. 4 shows the two sides of the same substrate of the same conductive moving target 7. Thus, FIG. 4 shows high-resolution segments 12 for the n-periodic receive coil pair 5, 6 and stacked target 11 for the 1-periodic absolute position receive coil pair 3, 4.

[0059] FIG. 5 shows a third embodiment of a conductive moving target 7. The third embodiment of the conductive moving target 7 shown in FIG. 5 differs from the second embodiment of the conductive moving target 7 shown in FIG. 4 in that the second element 11 has the shape of an arc segment of a full ring, which is arranged on the same side as the first element 10 comprising the segments 12. Furthermore, the first element 10 and the second element 11 of the conductive moving target 7 are arranged next to each other, particularly the second element 11 is arranged inside the first element 10, and the first element 10 and the second element 11 do not overlap.

[0060] FIG. 6 shows a fourth embodiment of a conductive moving target 7. The fourth embodiment of the conductive moving target 7 shown in FIG. 6 differs from the third embodiment of the conductive moving target 7 shown in FIG. 5 in that the second element 11 has a rectangular shape and overlaps with the first element 10. Particularly, the first element 10 comprising the segments 12 completely overlaps the second element 11 if the gaps between the segments 12 are considered to belong to the first element 10.

[0061] FIG. 7 shows a fifth embodiment of a conductive moving target 7. The fifth embodiment of the conductive moving target 7 shown in FIG. 7 differs from the fourth embodiment of the conductive moving target 7 shown in FIG. 6 in that the second element 11 has the shape of an arrow.

[0062] FIG. 8 shows a sixth embodiment of a conductive moving target 7, wherein the second element 11 has a bigger arrow shape compared to the fifth embodiment shown in FIG. 7.

[0063] FIGS. 9a and 9b show a target configuration comparisons for: [0064] a) Second embodiment of conductive moving target shown in FIG. 4 [0065] b) Third embodiment of conductive moving target shown in FIG. 5 [0066] c) Fourth embodiment of conductive moving target shown in FIG. 6 [0067] d) Fifth embodiment of conductive moving target shown in FIG. 7, and [0068] e) Sixth embodiment of conductive moving target shown in FIG. 8.

[0069] The setup of the used comparison was: [0070] Speed 1000 rpm [0071] Nominal AG 1 mm . . . 1.75 mm [0072] X/Y Displacement +/−0.3 mm [0073] Tilt +/−0 . . . 0.5 mm [0074] Different Targets were Tested

[0075] FIGS. 9a and 9b show a performance comparison based on 32× coil.

[0076] There are different ways of signal processing to calculate the absolute high resolution angle signal. One possible method is shown below.

[0077] Step1: Calculate Divisor=(Resolution/#HighResolutionPeriods)

[0078] Step2: Check the actual period

ActualPeriod=Quotient(AbsoluteAngle/Divisor)

[0079] Step3: Calculate the High Resolution Absolute Angle

AbsHighres=HighresAngle+ActualPeriod*Resolution

[0080] Step4: Check Plausibility and correct period if needed [0081] IF((AbsHighres−#HighResolutionPeriods*AngleLowRes))>Threshold->Output=AbsHighres−Resolution [0082] IF((AbsHighres−#HighResolutionPeriods*AngleLowRes))<-Threshold->Output=AbsHighres+Resolution [0083] ELSE Output =AbsHighres

[0084] FIG. 10 shows a high-resolution output after processing, particularly signal plot of 32 periodic high-resolution sensor and processed high resolution absolute sensor.

[0085] By implementing two or more sets of the high-resolution absolute sensors on one PCB it is possible to generate a redundant solution for higher diagnostic coverage.

[0086] By implementing two sets of the high-resolution absolute sensors on each side of a torsion bar it is possible to calculate the torque as the difference between the two sensors.

[0087] FIG. 11 shows a schematic view of a third embodiment of an inductive position sensor 1 according to the invention. The inductive position sensor 1 shown in FIG. 11 is a linear position sensor with a straight measurement area, along which the conductive target 7 moves. Otherwise, the third embodiment of the inductive position sensor 1 shown in FIG. 11 corresponds to the first embodiment of the inductive position sensor 1 shown in FIG. 1.