INDUCTIVE POSITION SENSOR AND METHOD FOR DETECTING A MOVEMENT OF A CONDUCTIVE TARGET

Abstract

An inductive position sensor and method for detecting a movement of a conductive target, having: at least a first and a second transmitter coil having the same shape and which are phase-shifted to each other, at least one oscillator for generating a first and a second transmitter signal having the same shape and which are phase shifted to each other and are applied to the first transmitter coil and second transmitter coil respectively, at least one receiver coil, and a processing unit for determining a phase-shift between the first or second transmitter signal and a receiver signal received at the receiver coil; the determined phase-shift corresponding to the position of the conductive target above the first and second transmitter coils.

Claims

1. An inductive position sensor for detecting a movement of a conductive target, comprising: at least a first transmitter coil and a second transmitter coil, wherein the first transmitter coil and the second transmitter coil have the same shape and are phase-shifted to each other, wherein the conductive target moves above the first transmitter coil and the second transmitter coil; at least one oscillator configured to generate a first transmitter signal and a second transmitter signal, wherein the first transmitter signal and the second transmitter signal have the same shape and are phase-shifted to each other and are applied to the first transmitter coil and second transmitter coil respectively; at least one receiver coil; and a processing unit configured to determine a phase-shift between the first transmitter signal or the second transmitter signal and a receiver signal received at the receiver coil, wherein the determined phase-shift corresponds to a position of the conductive target above the first transmitter coil and second transmitter coil.

2. The inductive position sensor according to claim 1, wherein the first transmitter coil and the second transmitter coil and/or the first transmitter signal and the second transmitter signal are phase-shifted by 90°.

3. The inductive position sensor according to claim 1, wherein the first transmitter coil and the second transmitter coil each comprise two wire loops, which are wound in opposite directions.

4. The inductive position sensor according to claim 1, wherein the first transmitter coil, the second transmitter coil and the at least one receiver coil are arranged on a substrate, and wherein the first transmitter coil and the second transmitter coil are superimposed.

5. The inductive position sensor according to claim 1, wherein the inductive position sensor is a radial position sensor and the conductive target is connected or connectable to a rotating shaft and the first transmitter coil, the second transmitter coil and the at least one receiver coil at least partially surrounding the rotating shaft, or wherein the inductive position sensor is a linear motion sensor and the conductive target can move along a movement path, and the first transmitter coil, the second transmitter coil and the at least one receiver coil are arranged along the movement path.

6. The inductive position sensor according to claim 1, further comprising: a zero-crossing comparator configured to detect zero-crossing of the first transmitter signal or the second transmitter signal and the receiver signal; and a counter configured to determine a delay between the zero-crossing of the first transmitter signal or the second transmitter signal and the receiver signal, wherein the processing unit is configured to determine the phase-shift between the first transmitter signal or second transmitter signal and the receiver signal for rising and falling edges of the first transmitter signal or the second transmitter signal and/or the receiver signal.

7. The inductive position sensor according to claim 1, further comprising: a zero-crossing comparator configured to detect zero-crossing of the first transmitter signal or the second transmitter signal and the receiver signal, wherein the processing unit in combination with the at least one oscillator are configured to adjust a phase of the first transmitter signal and the second transmitter signal, and wherein the processing unit is configured to use the zero-crossing comparator to change the phase of the first transmitter signal and the second transmitter signal, which is phase-shifted by 90° relative to the first transmitter signal, until the first transmitter signal or the second transmitter signal and the receiver signal have identical zero-crossings.

8. The inductive position sensor according to claim 1, further comprising a polarity inverter configured to invert a polarity of the receiver signal, wherein the processing unit is configured to determine the phase-shift between the first transmitter signal or the second transmitter signal and the receiver signal for the original polarity and the inverted polarity of the receiver signal and calculate an average to compensate for DC offsets in the receiver signal.

9. A method for detecting a movement of a conductive target, comprising: applying a first transmitter signal to a first transmitter coil and a second transmitter signal to a second transmitter coil, wherein the first transmitter coil and the second transmitter coil have the same shape and are phase-shifted to each other and wherein the first transmitter signal and the second transmitter signal have the same shape and are phase-shifted to each other; receiving a receiver signal by at least one receiver coil; and determining a phase-shift between the first transmitter signal or the second transmitter signal and the receiver signal, wherein the determined phase-shift corresponds to a position of the conductive target above the first transmitter coil and the second transmitter coil.

10. The method according to claim 9, wherein the first transmitter coil and the second transmitter coil each comprise two wire loops, which are wound in opposite directions.

11. The method according to claim 9, wherein the first transmitter coil, the second transmitter coil and the at least one receiver coil are arranged on a substrate, wherein the first transmitter coil and the second transmitter coil are superimposed.

12. The method according to claim 9, further comprising: detecting a rotational movement of the conductive target around a rotating shaft, wherein the first transmitter coil, the second transmitter coil and the at least one receiver coil at least partially surround the rotating shaft, or detecting a linear motion of the conductive target along a movement path, wherein the first transmitter coil, the second transmitter coil and the at least one receiver coil are arranged along the movement path.

13. The method according to claim 9, comprising: detecting a zero-crossing of the first transmitter signal or the second transmitter signal and the receiver signal; determining a delay between the zero-crossing of the first transmitter signal or the second transmitter signal and the receiver signal, based on a counter signal; detecting rising and falling edges of the first transmitter signal or the second transmitter signal and/or the receiver signal; and determining the phase-shift between the first transmitter signal or the second transmitter signal and the receiver signal for rising and falling edges of the first transmitter signal or the second transmitter signal and/or the receiver signal.

14. The method according to claim 9, comprising: detecting zero-crossing of the first transmitter signal or the second transmitter signal and the receiver signal; and adjusting a phase of the first transmitter signal and the second transmitter signal, wherein the phase of the first transmitter signal and the second transmitter signal, which is phase-shifted by 90° relative to the first transmitter signal, is changed until the first transmitter signal or the second transmitter signal and the receiver signal have identical zero-crossings.

15. The method according to claim 9, comprising: inverting a polarity of the receiver signal; determining the phase-shift between the first transmitter signal or the second transmitter signal and the receiver signal for the original polarity and the inverted polarity of the receiver signal; and calculating an average to compensate for DC offsets in the receiver signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] In the following, the invention will be further explained with respect to the embodiments shown in the figures. It shows:

[0082] FIG. 1 a block diagram of an inductive position sensor according to a first embodiment,

[0083] FIGS. 2A-D different conditions of the transmitter coils and receiver coil of the inductive position sensor,

[0084] FIG. 3 exemplary transmitter and receiver signals for an inductive position sensor with a conductive target at 0°,

[0085] FIG. 4 exemplary transmitter and receiver signals for an inductive position sensor with a conductive target at 90°,

[0086] FIG. 5 exemplary transmitter and receiver signals for an inductive position sensor with a conductive target at 180°,

[0087] FIG. 6 exemplary transmitter and receiver signals for an inductive position sensor with a conductive target at 270°,

[0088] FIG. 7 a block diagram of an inductive position sensor according to a second embodiment,

[0089] FIG. 8 a block diagram of an inductive position sensor according to a third embodiment, and

[0090] FIG. 9 a block diagram of an inductive position sensor according to a fourth embodiment.

DETAILED DESCRIPTION

[0091] FIG. 1 shows a block diagram of an inductive position sensor 1 for detecting a movement of a conductive target 2 according to a first embodiment. The inductive position sensor 1 shown in FIG. 1 is a radial position sensor, which detects a rotational movement of the conductive target 2. The conductive target 2 for example is a metal plate covering 180° around the rotational axis of the conductive target 2.

[0092] The inductive position sensor 1 comprises a first transmitter coil 3 and a second transmitter coil 4. The first transmitter coil 3 and the second transmitter coil 4 have the same shape and are phase-shifted to each other. For example, the first transmitter coil 3 and the second transmitter coil 4 are phase-shifted by 90°, like for a first sine transmitter coil 3 and a second cosine transmitter coil 4. The conductive target 2 moves above the first transmitter coil 3 and second transmitter coil 4.

[0093] Each of the first transmitter coil 3 and the second transmitter coil 4 comprise two wire loops (A, B, C, D), which are wound in opposite directions, as will be explained below in detail with respect to FIGS. 2A-D.

[0094] The inductive position sensor 1 according to the first embodiment shown in FIG. 1 comprises a first oscillator 5A for the first transmitter coil 3 and a second oscillator 5B for the second transmitter coil 4. The first oscillator 5A connected to the first transmitter coil 3 generates a first transmitter signal 6 and the second oscillator 5B connected to the second transmitter coil 4 generates a second transmitter signal 7. The first transmitter signal 6 and the second transmitter signal 7 have the same shape and are phase-shifted to each other. The first transmitter signal 6 and the second transmitter signal 7 can be shifted by 90°, like in case of a first sine transmitter signal 6 and a second cosine transmitter signal 7. The first transmitter signal 6 is applied to the first transmitter coil 3 and the second transmitter signal 7 is applied to the second transmitter coil 4.

[0095] The inductive position sensor 1 of FIG. 1 further comprises a receiver coil 8. The receiver coil 8 surrounds the first transmitter coil 3 and the second transmitter coil 4.

[0096] The first transmitter coil 3, the second transmitter coil 4 and the receiver coil 8 are partly covered by the conductive target 2. The first transmitter signal 6 applied to the first transmitter coil 3 and second transmitter signal 7 applied to the second transmitter coil 4 generate a superimposed electromagnetic field. This electromagnetic field is picked-up by the receiver coil 8, which in turn provides a receiver signal 10. The receiver signal 10 depends on the position of the conductive target 2, as the superimposed electromagnetic field generated by the first transmitter coil 3 and the second transmitter coil 4 induces eddy currents in the conductive target 2, which in turn changes the electromagnetic field picked-up by the receiver coil 8. For example, the phase of the receiver signal 10 changes with the position of the conductive target 2.

[0097] The first transmitter coil 3, the second transmitter coil 4 and the receiver coil 8 are arranged on a substrate 11. The substrate 11 is for example a printed circuit board and the first transmitter coil 3, the second transmitter coil 4 and the receiver coil 8 are formed by copper traces on the substrate.

[0098] The first transmitter coil 3 and the second transmitter coil 4 are superimposed, to generate a superimposed electromagnetic field. For example, the first transmitter coil 3 and the second transmitter coil 4 are arranged in the same area of the substrate 11, but on different layers.

[0099] The inductive position sensor 1 of FIG. 1 further comprises a processing unit 9 for detecting a phase-shift between the first transmitter signal 6 or the second transmitter signal 7 and the receiver signal 10 received at the receiver coil 8. Since the phase-shift between the first transmitter signal 6 and the second transmitter signal 7 is fixed, i.e., does not change, it is sufficient to detect the phase-shift between the first transmitter signal 6 or second transmitter signal 7 and the receiver signal 10. The determined phase-shift corresponds to the position of the conductive target 2 above the first transmitter coil 3 and the second transmitter coil 4.

[0100] The phase-shift between the first transmitter signal 6 or the second transmitter signal 7 and the receiver signal 10 can be determined by different methods. For example, a zero-crossing comparator 13 can be used to detect zero-crossing of the first transmitter signal 6 or the second transmitter signal 7 and of the receiver signal 10. Based on the zero-crossing of the first transmitter signal 6 or the second transmitter signal 7 and the receiver signal 10, the phase-shift can be determined, as will be explained in more detail below.

[0101] The first oscillator 5A and second oscillator 5B, the zero-crossing comparator 13, the processing unit 9 and optional further analog signal processing components 16 like filter, gain setting circuit or similar can be contained in an integrated circuit (IC) chip 15, which is also arranged on the substrate 11, for example, soldered on the substrate 11.

[0102] FIGS. 2A-D shows different conditions of the first transmitter coil 3, the second transmitter coil 4 and the receiver coil 8 of the inductive position sensor 1.

[0103] FIG. 2A shows the first transmitter coil 3 and the receiver coil 8. The second transmitter coil 4 has been neglected for clarity purposes in FIG. 2A. The first transmitter coil 3 comprises two wire loops A and C, which are wound in opposite directions, clockwise and counterclockwise, depending on the current flowing in them. For example, in FIG. 2A the current in loop A is flowing counterclockwise, while in loop C it is flowing clockwise. Reversing the polarity of the voltage applied to the terminals of the first transmitter coil 3, as shown in FIG. 2B, also reverses the current flow which creates a clockwise current flow in loop A and a counterclockwise current flow in loop C. By applying the “left hand rule,” one can see that the fields generated in loops A and C are always of opposite polarity. Symbol ⊙ indicates a positive magnetic field flowing out of the plane of view and symbol .Math. indicates a negative magnetic field flowing into the plane of view. Consequently, if no conductive target 2 is placed above or below the first transmitter coil 3, the resulting secondary voltage V.sub.RX, picked-up by the secondary receiver coil 8 that surrounds the first transmitter coil 3 and the second transmitter coils 4 is zero as the two fields A and C cancel each other.

[0104] FIG. 2C shows the second transmitter coil 4 and the receiver coil 8. The first transmitter coil 3 has been neglected for clarity purposes in FIG. 2C. The second transmitter coil 4 comprises two wire loops B and D, which are wound in opposite directions, clockwise and counterclockwise, depending on the current flowing in them. For example, in FIG. 2C the current in loop B is flowing counterclockwise, while it is flowing clockwise in loop D. Reversing the polarity of the voltage applied to the terminals of the second transmitter coil 4, as shown in FIG. 2D, also reverses the current flow which creates a clockwise current flow in loop B and a counterclockwise current flow in loop D.

[0105] By applying the “left hand rule,” one can see that the fields generated in loop B and loop D are always of opposite polarity. Symbol ⊙ indicates a positive magnetic field flowing out of the plane of view and symbol .Math. indicates a negative magnetic field flowing into the plane of view. Consequently, if no conductive target 2 is placed above or below the second transmitter coil 4, the resulting secondary voltage V.sub.RX, picked up by the receiver coil 8 that surrounds the first transmitter coil 3 and the second transmitter coil 4 is zero as the two fields B and D cancel each other.

[0106] By superimposing the first transmitter coil 3 and the second transmitter coil 4 and applying the first transmitter signal 6 to the first transmitter coil 3 and 90° phase-shifted the second transmitter signal 7 to the second transmitter coil 4, a rotating magnetic field is generated. As long as no conductive target 2 is placed above or below the first transmitter coil 3 and the second transmitter coil 4, the receiver signal 10 remains zero as all fields combined cancel each other.

[0107] FIG. 3 shows exemplary of the first transmitter signal 6 and the second transmitter signal 7 and the receiver signal 10 for the inductive position sensor 1 with the conductive target 2 at 0°.

[0108] FIG. 4 shows exemplary of the first transmitter signal 6 and the second transmitter signal 7 and the receiver signal 10 for the inductive position sensor 1 with the conductive target 2 at 90°.

[0109] FIG. 5 shows exemplary of the first transmitter signal 6 and the second transmitter signal 7 and the receiver signal 10 for the inductive position sensor 1 with the conductive target 2 at 180°.

[0110] FIG. 6 shows exemplary of the first transmitter signal 6 and the second transmitter signal 7 and the receiver signal 10 for the inductive position sensor 1 with the conductive target 2 at 270°.

[0111] As can be seen from FIGS. 3 to 6 the phase of the receiver signal 10 continuously changes with the position of the conductive target 2 above the first transmitter coil 3, the second transmitter coil 4 and the receiver coil 8. By determining the phase-shift of the receiver signal 10 to either the first transmitter signal 6 or the second transmitter signal 7 the position of the conductive target 2 is known.

[0112] FIG. 7 shows a block diagram of an inductive position sensor 1 according to a second embodiment. The inductive position sensor 1 shown in FIG. 7 is a linear motion position sensor. A conductive target 2 can move along a movement path 12 and a first transmitter coil 3, a second transmitter coil 4 and a receiver coil 8 are arranged along the movement path 12. The movement path 12 can be divided into 360 steps, i.e., from 0° to 360°, as for the inductive position sensor 1 shown in FIG. 1. However, the movement path 12 can be alternatively divided based on any other length scale.

[0113] In all other aspects, the second embodiment shown in FIG. 7 corresponds to the first embodiment shown in FIG. 1.

[0114] FIG. 8 shows a block diagram of an inductive position sensor 1 according to a third embodiment. This embodiment differs from the first embodiment shown in FIG. 1 in that a counter 14 is used to determine the phase-shift between a first transmitter signal 6 or a second transmitter signal 7 and a receiver signal 10. The counter 14 is for example started at the rising or falling edge of the first transmitter signal 6 at the zero-crossing and stopped when the respective rising or falling edge of the receiver signal 10 has its zero-crossing.

[0115] FIG. 9 shows a block diagram of an inductive position sensor 1 according to a fourth embodiment. According to this fourth embodiment, a processing unit 9 in combination with a first oscillator 5A and a second oscillator 5B can adjust the phase of a first transmitter signal 6 and a second transmitter signal 7. The processing unit 9 uses a zero-crossing comparator 13 to change the phase of the first transmitter signal 6 and the second transmitter signal 7, which can be phase-shifted by 90° relative to the first transmitter signal 6, until the first transmitter signal 6 or the second transmitter signal 7 and a receiver signal 10 have identical zero-crossings. The phase change applied to the first transmitter signal 6 and the second transmitter signal 7 by adjusting the first oscillator 5A and the second oscillator 5B corresponds to the position of the conductive target 2.