Inductive position sensor

Abstract

Inductive position sensor comprising a first position transducer and a second position transducer and one or more transmitter coils, wherein each said position transducer comprises: at least two receiver coils which are spatially out of phase and to be excited by said one or more transmitter coils, and a movable target arranged to inductively couple between said one or more transmitter coils and said receiver coils so that signals are generated on the receiver coils dependent on the position of the target relative to the receiver coils; wherein the period length of the receiver coils of the second transducer is an even integer multiple of the period length of the receiver coils of the first transducer; wherein the target of the first transducer comprises one or more pairs of target parts, wherein the pairwise distance between centres of the target parts is equal to one period, or a multiple thereof, of the receiver coils of the first transducer, and the pairwise length of the target parts is equal.

Description

D E S C R I P T I O NINDUCTIVE POSITION SENSORTECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of inductive position sensors, which are based on coupled coils.BACKGROUND

[0002] Available publications show mostly absolute linear or rotary position sensors based on the inductive principle.

[0003] Document EP3988903A1 discloses a position sensor system, particularly inductive position sensor system, comprising at least two receiver coil sets, at least one transmitter coil and a signal conditioning and processing unit, wherein in each receiver coil set comprises at least two separate receiver coils, particularly a sine receiver coil and a cosine receiver coil, which is characterized in that the signal conditioning and processing unit is contained in a single integrated circuit and that the at least two receiver coil sets, the at least one transmitter coil and the integrated circuit containing the signal conditioning and processing unit are located on a single printed circuit board.

[0004] Document US20100319467A1 relates to an inductive torque sensor, Inductive torque sensor, in particular for a motor vehicle, comprising at least one excitation coil, at least one oscillator circuit which is coupled with the excitation coil and which generates a periodic alternating voltage signal and couples it into the excitation coil during operation, A stator circuit board with a first receiver means and a second receiver means, which each have a number of periodically repeated receiver structures, at least 2 rotors which can be rotated relative to one another and relative to the stator circuit board and which influence the strength of the inductive coupling between the excitation coil and the receiver means, Evaluation means suitable for the evaluation of the signals induced in the receiver means, wherein the number N of the receiver structures of the first receiver means and the number M of the receiver structures of the second receiver means are in an integer ratio relative to one another.

[0005] Document GB2503006A discloses a number of position sensors. The position sensors are arranged to inductively sense the position of a target relative to a number of sensor coils. The target is arranged to magnetically couple with first and second coils so that signals are generated that depend on the relative position of the target and the first and second coils. The target extends along the measurement path and is inclined relative to the measurement path so that substantially all of the target overlaps with loops of the first coil and so that when a first end of the target is adjacent a first loop of the first coil, a second end of the target is adjacent a second loop of the first coil that has an opposite winding direction to that of the first loop. The second coil is arranged relative to the target such that the magnetic coupling between the second coil and the first end of the target is opposite to the magnetic coupling between the second coil and the second end of the target.

[0006] Document WO2023037152 describes an inductive positioning sensor for small electrical and electronic applications that allows to achieve a higher induced voltage output. The described inductive positioning sensor is arranged in a multi-layer printed circuit board, that comprises an excitation coil and at least one receiver coil A and a corresponding duplicated receiver coil A, where the excitation coil circularly surrounds the limits defined by the at least one receiver coil A and the corresponding duplicated receiver coil A. The at least one receiver coil A comprises a main convergence point and at least one auxiliary convergence point, and the corresponding duplicated receiver coil A comprises at least one auxiliary convergence point. The at least one receiver coil A and the corresponding duplicated receiver coil A merge together in a secondary convergence point. These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.GENERAL DESCRIPTION

[0007] The present disclosure discloses a contributes to inductive position sensors, which are based on coupled coils. A sensor for an absolute position measurement can be divided into three main parts: the coil system comprising at least one transmitter (Tx) coil and at least two receiver (Rx) coils, a moving coupling-element (target) and a signal processing circuitry. The coils are planar coils on a printed-circuit-board (PCB), which isnormally mounted at a fixed position. The target is mounted on the moving part, whose position is supposed to be measured.

[0008] The transmitter coil of the coil system is driven by an oscillator circuit and therefore generates an alternating magnetic field. Due to the special differential geometry of the receiver coils, the induced voltage is zero without the target. Only with the (conductive) target an induced voltage can be measured at the receiver coils, since Foucault-currents will occur in the target, which are causing an opposing field to the transmitter field (Lenz law). For the resultant magnetic field, the induced voltage at the receiver coils doesn't cancel out and therefore the induced voltage amplitude depends on the target position. To be more accurate, the target position is amplitude modulated onto the alternating voltage signal, which will oscillate according to the Tx frequency and can be measured on the receiver coils.

[0009] Besides the coil system, the PCB contains various electronic components like capacitors and resistors, together with an application-specific-integrated-circuit (ASIC). The ASIC is needed as a driver for the Tx oscillator circuit and for the Rx voltage measurement, which includes demodulation, amplification and optional filtering of the sensor signals. Commonly, the ASIC has at least two output channels in quadrature, a sine and a cosine channel, which form a vector in the complex plane. Alternatively, a digital output signal (e.g. SENT interface) can be used. The input to the ASIC (signals from the coils) are at least two channels in quadrature after demodulation. For three-phase coil systems, the Clarke transform may need to be applied. The angle of the output vector, which can be calculated based on the arctangent function, gives information about the absolute linear position of the target. This means that between the calculated angle and the actual target position exists a linear relationship.

[0010] The present disclosure focuses on a differential position measurement between two moving parts. For the differential measurement principle, most publications are about rotary position sensing, since a differential angle is needed for a torque measurement and torque-sensors are in great demand.

[0011] A differential position can be obtained by using two independent linear position sensors. In orderto save space and costs, the present disclosure combines two inductive linear position sensors in one part. One of the main problems addressed is the mutualcoupling of the two coil-systems, as both systems are placed on the same area of the PCB, and therefore, the magnetic fields are interfering.

[0012] In order to minimize the "crosstalk", an accuracy error introduced by the interference of the two coil systems, we choose a preferred ratio of 2:1 between the receiver coil periodicities, under the constraint of specific target widths and center distances. For inductive differential rotary position sensors an arguably similar concept is already the state of the art. However, the same concept cannot be used for linear (or partial rotary) position sensing applications, since it does not eliminate cross-talk when the receiver coil system does not span the entire 360-degree range. Likewise, with our new linear differential position sensor design, this ratio gives the optimal sensor accuracy and receiving amplitude.

[0013] The present disclosure discloses an inductive position sensor comprising a first position transducer and a second position transducer and one or more transmitter coils, wherein each said position transducer comprises: at least two receiver coils which are spatially out of phase and to be excited by said one or more transmitter coils, and a movable target arranged to inductively couple between said one or more transmitter coils and said receiver coils so that signals are generated on the receiver coils dependent on the position of the target relative to the receiver coils; wherein the period length of the receiver coils of the second transducer is an even integer multiple of the period length of the receiver coils of the first transducer; wherein the target of the first transducer comprises one or more pairs of target parts, wherein the pairwise distance between centres of the target parts is equal to one period, or a multiple thereof, of the receiver coils of the first transducer, and the pairwise length of the target parts is equal.

[0014] Typically, there is either exactly one transmitter coil shared between both receiver coils, or several transmitter coils for the individual transducers.

[0015] Typically, inductive position sensors have receiver coils which are spatially out of phase as is commonly and generally known in the art.

[0016] Typically, as is commonly and generally known in the art, a receiver coil is designed to be differential, therefore without a target the induced voltage in the receiver coil is ideally equal to zero. Only with the presence of the target, the modified coupling between transmitter and receiver results in an induced voltage in the receivercoils. Typically, as is commonly and generally known in the art, demodulation of the receiver signals, from high-frequency of the excitation to a low-frequency output signal is dependent on target position.

[0017] Typically, as is commonly and generally known in the art, signals are induced AC voltages in the receiver coils.

[0018] Typically, the period length is their effective electromagnetic period for inductive purposes.

[0019] Typically, partitioning is carried out in movement direction. The partitioning can be done either by complete separation of the material or by the significant part of the geometric shape, such that separate effective electromagnetic targets occur. Typically, the target part centre is their effective electromagnetic target part centre for inductive purposes.

[0020] Typically, the length of the target parts is their effective electromagnetic length for inductive purposes. Typically, it can vary by +-5% or a fixed distance (e.g. a few skindepths).

[0021] Typically, the dimensions of the period lengths, pairwise centre distances, among others, can have small systematic deviations which are useful in practice and typically used to reduce cross-coupling and angular error, for example up to +-0.2mm or +-5%, as is commonly known in the art.

[0022] In an embodiment, the target of the second transducer comprises one or more pairs of target parts, wherein the pairwise distance between centres of the target parts is equal to half a period, or a multiple plus half thereof, of the receiver coils of the first transducer, and the pairwise length of the target parts is equal.

[0023] The disclosed sensor can be referred as a planar sensor as it comprises one or more PCB-based planar coils.

[0024] The movable target is arranged to magnetically couple at excitation frequencies typically in the range of 1 MHz and 10 MHz, for example 4 MHz, but may go beyond these limits.

[0025] A multiple number can be defined as a number that may be divided by another a certain number of times without a remainder.

[0026] The target length can be defined as a length of an extension of the target which effectively couples between transmitter and receiver coils so that signals are generated on the receiver coils dependent on the position of the target relative to the receiver coils.

[0027] In an embodiment, the first position transducer and the second position transducer can be partially or fully overlapping.

[0028] In an embodiment the target can be a conductor, ferromagnetic or an electromagnetic coil, in particular made of stainless steel, aluminium or copper.

[0029] In an embodiment, the inductive position sensor further comprises an oscillator circuit which is coupled with the one or more transmitter coils for generating a periodic alternating voltage signal and exciting the coil during operation.

[0030] In an embodiment, the receiver coils are planar coils.

[0031] In an embodiment, the transmitter coil is a planar coil.

[0032] In an embodiment, the receiver and / or transmitter coils are on a printed-circuit- board, in particular a flexible printed-circuit-board.

[0033] In an embodiment, the receiver coils and the one or more transmitter coils are arranged in a fixed position.

[0034] In an embodiment, the length of the target parts of the first transducer is equal to half a period of the receiver coils of the first transducer.

[0035] In an embodiment, the length of the target parts of the second transducer is equal to half a period, of the receiver coils of the first transducer.

[0036] In an embodiment, the target parts, when adjacent, are integrally formed by a same physical piece.

[0037] It is also disclosed a linear inductive position sensor according to any of the previous embodiments wherein the movable target is linearly movable.

[0038] It is also disclosed a rotary inductive position sensor according to any of the previous embodiments wherein the movable target is rotatable.

[0039] In an embodiment, the inductive position sensor according to any of the previous embodiments can comprise a data processor arranged to obtain an angle, for each transducer, which is dependent on the position of the target relative to the receiver coils, from the signals generated on the receiver coils, in particular by calculating an arctangent of the demodulated digitized signals generated on the receiver coils.

[0040] In an embodiment, the data processor is further arranged to obtain a differential angle from the difference between the obtained angles of each transducer.

[0041] It is also disclosed a method to determine a differential position between inductive position sensor targets with an inductive position sensor according to any of the preceding embodiments comprising the steps of: exciting said one or more transmitter coils; measuring target angles from the receiver coils; subtracting the measured target angles to obtain the differential position between the inductive position sensor targets.BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0043] Figure 1: Isometric view of an embodiment of complete sensor (one transmitter coil for both coil-systems).

[0044] Figure 2: Top view of an embodiment with hidden targets and sine receiver coils.

[0045] Figure 3: Schematic representation of an embodiment with a working principle in the preferred Variant with a 2:1 period ratio.

[0046] Figure 4: Schematic representation of an embodiment with a working principle in the preferred Variant with a 2:1 period ratio for the differential sensor.

[0047] Figure 5: Schematic representation of an embodiment with a working principle in the preferred Variant with a 2:1 period ratio for the differential sensor.

[0048] Figure 6: Schematic representation of an embodiment with a generalization of the measurement concept: the RX coils have a period ratio of 4:1.

[0049] Figure 7: Schematic representation of an embodiment of the present disclosure.

[0050] Figure 8: Schematic representation of an embodiment of the present disclosure.

[0051] Figure 9: Schematic representation of an embodiment of the present disclosure.DETAILED DESCRIPTION

[0052] The present disclosure relates to an inductive position sensor.

[0053] In one embodiment of the disclosure, illustrated in Figure 1 and Figure 2 showing an example sensor design. The receiver coil periodicity of coil-system 1 is p = 5 and the periodicity of coil-system 2 is p = 10. Targets can be on one side of the sensor, or on opposite site

[0054] As illustrated in Figure 1, an isometric view of complete sensor (one transmitter coil for both coil-systems) wherein 1 represents a receiver coils; 2 represents a transmitter coil; 3 represents a processing circuitry; 4 represents a first target and 5 represents a second target.

[0055] In one embodiment of the disclosure, illustrated in Figure 2, a top view with hidden targets and sine receiver coils is showed, wherein 6 represents one period of the cosine coil (Rx) of coil-system 1; 7 represents a receiver coil (cos) of coil-system 1; 8 represents a transmitter coil; 9 represents a receiver coil (cos) of coil-system 2 and 10 represents one period of the cosine coil (Rx) of coil-system 2.

[0056] Description of working principle in the preferred variant with a 2:1 ratio of period lengths: Coils possess neighbouring "parts" with opposite winding direction, meaning without any target any induced eddy currents would be cancelled. If a target is placed on one part of the coils, one gets maximum signal, as illustrated in Figure 3A.

[0057] If the target is placed with equal area on top of two coil "parts" with opposite winding, signal is 0, as illustrated in Figure 3B.

[0058] For the differential sensor, the targets are designed to make signal in one coil, and no signal in the other one - as the latter one has always regions with opposite winding direction covered independent on target position. Examples are, as illustrated in Figure 4.

[0059] The target must not have necessarily the same width as the coil periodicity. Other widths can be used to decrease the linearity error, enhance the amplitude or optimize mechanical design, as illustrated in Figure 5. In an embodiment, the target width equals the periodicity since the "standard" configuration is a target, which covers one Rx winding (one half Rx-period).

[0060] Assumption: The periodicity of coil system 1 is larger than coil system 2, i.e., the period of coil system 1 is shorter (in units of length) than the period of coil system 2. This is simply a naming convention and does not represent a restriction of the design.

[0061] The following conditions must be met for the measurement principle:

[0062] Coil periods: Under the above convention, the period of coil system 2 must be an even integer multiple of the period of coil system 1.

[0063] Transducing Element 1 (for measurement system 1):The transducing element of measurement system 1 consists of at least two inductive targets, where the total number of targets is even.The pairwise distance between the centers of the targets of measurement system1 is equal to one full period or an integer multiple thereof of the RX coil(s) of measurement system 2.(The length of the targets for measurement system 1 is pairwise equal).

[0064] Transducing Element 2 (for measurement system 2):The transducing element of measurement system 2 consists of at least one inductive target;The length of the target(s) for measurement system 2 is equal to one full period or an integer multiple thereof of the RX coil(s) of measurement system 1.(The center distance of the targets of measurement system 2 is equal to one full period of the RX coil(s) of measurement system 2).

[0065] Small deviations of the target lengths and center distances from the above stated requirements may be used to optimize the angular error of the measurement.

[0066] One of the main purposes of the disclosure is to prevent an interaction between transducing element 1 and coil system 2, as well as transducing element 2 and coil system 1. The targets may be connected by conductive material as shown in the examplecoil layouts, however we still consider them to be "separate" for description of the measurement principle.

[0067] The present disclosure can be used for a differential position signal to control an electric motor for braking force boosting in a braking system. One target is attached to the input rod (moved by driver by actuating the pedal). The other target is attached to a brake boosting part moved by an electric motor. The motor is controlled utilizing the differential stroke between the two targets. Typically, it is controlled to be a constant differential stroke.

[0068] Figure 6 shows an embodiment where additional (i.e. optional) target parts may be added. This has the advantage of improving signal and accuracy.

[0069] One embodiment of the disclosure, illustrated in Figure 7, shows an example of sensor design, wherein 4 represents a first target corresponding to half period of the cosine coil of a first receiver coil (7) and 5 represents a second target corresponding to half period of the cosine coil of a second receiver coil (9) of coil-system.

[0070] Using the differential position signal to control an electric motor for braking force boosting in a braking system. One target is attached to the input rod (moved by driver by actuating the pedal). The other target is attached to a brake boosting part moved by an electric motor. The motor is controlled utilizing the differential stroke between the two targets. Typically, it is controlled to be a constant differential stroke.

[0071] In an embodiment, target centers can be geometric center and / or shape of target parts (typically mostly rectangular). Centers and target parts should have a reference.

[0072] Figure 8 shows an embodiment of a circuit of an inductive position sensor according to the invention. This circuit comprises a first position transducer and a second position transducer and one transmitter coil. Each said position transducer comprises two receiver coils which are spatially out of phase and to be excited by said transmitter coil, and movable target arranged to inductively couple between said one or more transmitter coils and said receiver coils so that signals are generated on the receiver coils dependent on the position of the target relative to the receiver coils. A driving circuit drives the transmission coil. The signal from each transducer is amplified anddemodulated by the Demodulator / Amplifier. The two transducer signals are fed to an angle calculator (DSP) that provides a differential angle measurement.

[0073] Figure 9 shows an embodiment of the angle difference calculator where the input angles are subject to a modulus calculation (pl. P2) for removing whole periods, thus only remaining the overflow. The difference from these overflows is scaled (sl2) and an optional offset is applied (+offset). The final signal (diff_12) is output to be used.

[0074] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0075] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above-described embodiments are combinable. The following claims further set out particular embodiments of the disclosure.

Claims

C L A I M S1. Inductive position sensor comprising a first position transducer and a second position transducer and one or more transmitter coils, wherein each said position transducer comprises: at least two receiver coils which are spatially out of phase and to be excited by said one or more transmitter coils, and a movable target arranged to inductively couple between said one or more transmitter coils and said receiver coils so that signals are generated on the receiver coils dependent on the position of the target relative to the receiver coils; wherein the period length of the receiver coils of the second transducer is an even integer multiple of the period length of the receiver coils of the first transducer; wherein the target of the first transducer comprises one or more pairs of target parts, wherein the pairwise distance between centres of the target parts is equal to one period, or a multiple thereof, of the receiver coils of the first transducer, and the pairwise length of the target parts is equal.

2. Inductive position sensor according to the previous claim wherein the target of the second transducer comprises one or more pairs of target parts, wherein the pairwise distance between centres of the target parts is equal to half a period, or a multiple plus half thereof, of the receiver coils of the first transducer, and the pairwise length of the target parts is equal.

3. Inductive position sensor according to any of the previous claims wherein the first position transducer and the second position transducer are partially or fully overlapping.

4. Inductive position sensor according to any of the previous claims wherein the target is a conductor or an electromagnetic coil, in particular made of stainless steel, aluminium or copper.

5. Inductive position sensor according to any of the previous claims further comprising an oscillator circuit which is coupled with the one or more transmitter coils for generating a periodic alternating voltage signal and exciting the coil during operation.

6. Inductive position sensor according to any of the previous claims wherein the receiver coils are planar coils and / or the one or more transmitter coils are planar coils.

7. Inductive position sensor according to any of the previous claims wherein the receiver and / or the one or more transmitter coils are on a printed-circuit-board, in particular a flexible printed-circuit-board.

8. Inductive position sensor according to the previous claim wherein the receiver coils and the one or more transmitter coils are arranged in a fixed position.

9. Inductive position sensor according to any of the previous claims wherein the length of the target parts of the first transducer is approximately equal to half a period of the receiver coils of the first transducer.

10. Inductive position sensor according to any of the previous claims wherein the length of the target parts of the second transducer is approximately equal to half a period, of the receiver coils of the first transducer.

11. Inductive position sensor according to any of the previous claims wherein the target parts, when adjacent, are integrally formed by a same physical piece.

12. Linear inductive position sensor according to any of the previous claims wherein the movable target is linearly or rotatably movable.

13. Inductive position sensor according to any of the previous claims comprising a data processor arranged to obtain an angle, for each transducer, which is dependent onthe position of the target relative to the receiver coils, from the signals generated on the receiver coils, in particular by calculating an arctangent of the demodulated digitized signals generated on the receiver coils.

14. Inductive position sensor according to the previous claim wherein the data processor is further arranged to obtain a differential angle from the difference between the obtained angles of each transducer.

15. Method to determine a differential position between inductive position sensor targets with an inductive position sensor according to any of the preceding claims comprising the steps of: exciting said one or more transmitter coils; measuring target angles from the receiver coils; subtracting the measured target angles to obtain the differential position between the inductive position sensor targets.

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