Planar linear inductive position sensor with edge effect compensation

Abstract

Planar linear inductive position sensor, including: a substrate (10); at least one voice coil (12, 14); a first sensor coil (16a, 16b) with opposite edges extending over the opposite edges of the voice coil (12, 14) along a linear axis along which a linear position of a conductive object is to be detected; a second sensor coil (18a, 18b) with opposite edges extending along the linear axis over opposite edges of the voice coil (12, 14); wherein the first (16a, 16b) and the second (18a, 18b) sensor coils have geometries selected such that equal opposite magnetic fields are induced in the first (16a, 16b) and the second (18a, 18b) sensor coils when a magnetic field generated by the voice coil (12, 14) is present and no conductive object (20) is near the first (16a, 16b) and the second sensor coils, and unequal opposite magnetic fields are induced in the first (16a, 16b) and the second sensor coils when the conductive object (20) is near the first (16a, 16b) and the second (18a, 18b) sensor coils, wherein a difference in the unequal opposite magnetic fields induced in the first (16a, 16b) and the second (18a, 18b) sensor coils is determined by the symmetric magnetic fields of the first (16a, 16b) and the second (18a, 18b) sensor coils is determined by the symmetric magnetic fields of the first (16a, 16b) and the second (18a, 18b) sensor coils is determined by the symmetric magnetic fields of the first (16a, 16b) sensor coils. 18b) Sensor coil induced, correlated with the position of the conductive object being measured (20).

Description

[0001] The present invention relates to position sensing technology and inductive position sensing technology. In particular, the present invention relates to a planar linear inductive position sensor with edge effect compensation. GENERAL STATE OF THE ART

[0002] Position sensors are a common component in automotive, industrial, and aerospace applications. Whenever safety is paramount, extremely robust and reliable position sensors are essential. Potentiometers are commonly used as position sensors. These are contact sensors and are prone to wear and noise. To avoid these drawbacks, non-contact sensors are used. These sensors are based on inductive, capacitive, optical, and Hall-effect principles. Optical encoders offer good resolution but result in higher costs and reliability issues in harsh or contaminated environments. Hall-effect sensors are sensitive to temperature and external magnetic fields. Capacitive sensors are highly sensitive to extreme environmental changes.

[0003] Inductive sensors are used to convert a linear displacement or angular movement of a conductive object into a proportional electrical signal, using currents generated by a magnetic field induced in one or more sensor coils. Some inductive position sensors include at least one primary coil that maintains an oscillating signal generating a magnetic field, and one or more secondary coils that receive the position information as currents induced by the magnetic field, depending on the position of the conductive object.

[0004] Conventional inductive position sensors are expensive and bulky because the oscillator and sensor coils are wound radially around a core. Planar inductive position sensors are cost-effective because the coils are arranged in a single plane on a printed circuit board.

[0005] Planar inductive sensors consist of one or more oscillator coils, two sensor coils, and a movable conductive object that influences the strength of the magnetic coupling between the oscillator coils and the sensor coils. An alternating current is induced by the oscillator coil(s). The magnitude and phase of this alternating current depend on the position of the object. Eddy currents through the conductive object cause a difference in the currents and voltages of the sensor coils. The sensor coils are configured so that, in a uniform magnetic field not influenced by a conductive object, the voltages and currents induced in the sensor coils cancel each other out.

[0006] Some prior art examples of planar inductive position sensors include US Patent Publication US 20050253576, US Patent No. 4,507,638, US Patent No. 6,522,128, US Patent No. 7,196,604, and WO2002097374. A planar inductive sensor comprising two sensor coils and a pair of oscillator coils wound around the sensor coils is disclosed in Application Note AN-S1412 “Inductive Sensor Coil Design Using LX3301A” (2017) by Microsemi Corporation of Chandler, AZ.

[0007] Document DE 10 2016 202 859 B3 discloses a rotary angle sensor. Document DE 10 2024 203 340 A1 (subsequently published) discloses a measurement acquisition device for an inductive sensor arrangement.

[0008] A disadvantage of available linear inductive planar position sensors is that an uneven magnetic field is always present at the sensor's edges. This uneven magnetic field at the sensor's edges causes an offset voltage to be induced in the sensor coils, which negatively affects the sensor's accuracy.

[0009] In general, edge effects in linear sensors can be minimized by placing the sensor coils far away from the oscillator coil edges; however, this technique is not feasible in space-constrained applications because it increases the size of the sensor board.

[0010] Referring first to Fig. Figure 1 shows a diagram illustrating an example of a prior art planar inductive linear position sensor 8 formed on a substrate 10, including an oscillator coil with a pair of oscillator coil segments 12 and 14 driven from a center tap, and a sine sensor coil formed from two 360° segments 16a and 16b, with segment 16a being driven from the left side of Fig. 1 begins at 0° (sin 0° = 0) and segment 16b starts from the left side of Fig. 1 at (-sin 0°=0) and connected at their endpoints 42, 44, a cosine sensor coil formed from two segments of opposite phase, shown in dashed lines with the reference digits 18a and 18b, with segment 18a being from the left side of Fig. 1 at 0° (cos 0° = 1) begins and segment 18b starts from the left side of Fig. A movable conductive measuring object 20 begins at 0° (-cos 0° = -1) and is connected at its ends by segments 46 and 48. The movable measuring object 20 is made of a conductive material and is preferably made of a material with relatively high electrical conductivity, such as copper or aluminum. The sine sensor coil 16a and 16b is shown with lines 22 and 24, and the cosine sensor coil 18a and 18b is shown with lines 26 and 28.

[0011] Experts in the field of technology will understand that, while the in Fig. In the configuration shown, a pair of oscillator coils 12 and 14 are used, which can conveniently be formed from a single coil derived from the reference digit 30, from which it is driven by a control signal and which has the end lines 32 and 34; other prior art configurations use a single oscillator coil driven by a suitable signal generator.

[0012] As known in the prior art, the two oscillator coils 12 and 14, the sine sensor coil segments 16a and 16b and the cosine sensor coil segments 18a and 18b can be formed as separate layers on the multilayer substrate 10 using conventional printed circuit board manufacturing techniques.

[0013] The oscillator signals can be generated by a sensor interface circuit, and the sampled signals can be received and processed by a sensor interface circuit, for example, a single integrated sensor interface circuit 36 ​​such as the LX3301A inductive sensor interface circuit available from Microsemi Corporation of Chandler, AZ. Such a sensor interface circuit may include a signal generator section 36a, which is used to generate the oscillator signal that is fed into one or more oscillator coils, and sensor circuits 36b and 36c for sensing the signals from the sine and cosine sensor coils, respectively. Capacitors 38 and 40 are coupled between the end leads 32 and 34 of the oscillator coils 12 and 14, respectively, and ground to form LC resonant circuits. A typical value for capacitors 38 and 40 may be about 1.2 nF.The oscillator signal represented as Vin is fed into the oscillator coil segments 12 and 14, the ends of which are in . Fig. 1, which is connected to the signal generator section 36a of the inductive sensor interface circuit 36 ​​at connections Osc. 1 and Osc. 2, is preferably a sine wave, and the frequency of the oscillator signals fed into the oscillator coils depends only on the inductance of the oscillator coils 12, 14 and the respective capacitance values ​​of the capacitors 38 and 40. A typical, non-limiting oscillator frequency range can be between approximately 1 MHz and approximately 6 MHz.

[0014] The voltage induced by the movable conductive measuring object 20 in one of the sine or cosine sensor coils is a time-dependent derivative of the magnetic current from Maxwell's equation E=−dφBdt

[0015] Faraday's law of induction uses the magnetic flux ΦB through a region of space enclosed by a wire loop. The magnetic flux is defined by a surface integral. ∅B=∫B.dA

[0016] An alternating current Io(t) is applied to the oscillator coil segments 12, 14, generating an alternating magnetic field Bt(t). The alternating magnetic field Bo(t) induces a current It(t) in the movable conductive test object 20, which in simplified form is a closed conductor loop. This current in turn generates an alternating magnetic field Bt(t) that opposes the excitation magnetic alternating field Bt(t).

[0017] From the superimposed alternating magnetic fields Bo(t) + Bt(t), a voltage is induced in each of the sine and cosine sensor coils, according to the relationship E=−d∅dt=−d∬((B0(t,x,y)−Bt(t,x,y)dAdt=−ddt∬(B0(t,x,y)dA+ddt∬(Bt(t,x,y))dA where A represents a surface area of ​​the respective sensor coil.

[0018] It should be noted that each of the sensor coils has two surfaces, a positive and a negative lobe, pointing in opposite directions. The voltage induced in the positive lobe is Ep, and the voltage induced in the negative lobe is En. It follows that for a sensor coil with a symmetrical coil geometry, as found in Fig. As can be clearly seen in Figure 2, the section of the induced voltage caused by the oscillator coil segments 12 and 14 is zero; that is to say ddt∬B0(t,x,y)dA=0 dh, Ep−En=0

[0019] When a current-carrying conductor is connected in parallel to another conductor, magnetic coupling occurs between the two conductors, generating an additional induced voltage. Since the ends of the sine-sensor coil segments 16a and 16b, which are closest to the end sections of the oscillator coil segments 12 and 14, are connected at points 42 and 44, they have very few, if any, conductors of significant length close enough to form parallel conductors that are magnetically coupled to the conductors forming the end sections of the oscillator coils 12 and 14.

[0020] In the case of the cosine sensor coil segments 18a and 18b, an edge effect always results from their end segments 46 and 48, which are provided to connect the cosine segments 18a and 18b at their ends, as shown in Fig. Figure 3 shows that these end segments 46 and 48 are aligned parallel to the conductors that form the end sections of the oscillator coils 12 and 14 and are magnetically coupled to these conductors. This coupling results in an additional induced voltage (Ep + ΔEp) being coupled from the oscillator coils 12 and 14 into the positive lobes of the cosine coils 18a and 18b, compared to the voltage (En) induced in the negative lobe of the cosine sensor coils 18a and 18b. This always induces an offset voltage ΔEp in the sensor coil. ddt∬B0(t,x,y)dA≠0 dh, (Ep+ΔEp)−En≠0

[0021] The asymmetrically generated voltage at the cosine sensor coil adds the offset voltage to the voltage coupled to the moving object being measured. This complicates further processing of the signal and leads to significant measurement errors.

[0022] Fig. Figure 4 is an amplitude-position diagram of demodulated waveforms of the planar inductive linear position sensor 8. Fig. 1, which detects the waveform 50 from the sine sensor coil 16a and 16b and the waveform from the cosine sensor coil 18a and 18b of the sensor of Fig. 1 captured waveform displays 52. As in Fig. As can be seen in figure 4, there is an induced offset voltage, which is present at the reference digit 54 in the demodulated cosine waveform 52 of Fig. 4 is indicated. SUMMARY

[0023] According to the present invention, a linear inductive planar position sensor provides a highly accurate linear position by compensating for edge effects within an optimized spatial structure. Edge effects are eliminated by configuring the length of the oscillator coils so that they lie within the longitudinal edges of the sensor coils. The minimal space requirement offers the advantage of lower costs, as the printed circuit board (PCB) is smaller. The linear inductive planar position sensor of the present invention can also be implemented in multilayer printed circuit boards.

[0024] The linear inductive planar position sensor of the present invention is robust because it has no moving electrical contacts, exhibits good temperature performance, and is highly insensitive to dust. The linear inductive planar position sensor of the present invention is an absolute position sensor, meaning that it does not require any movement to determine its position when switched on.

[0025] The linear inductive planar position sensor of the present invention provides improved accuracy and space utilization compared to conventional planar position sensors. The linear inductive planar position sensor of the present invention is suitable for spatially limited and cost-effective applications. These applications include brake pedals, levers, and actuators, etc.

[0026] The linear inductive planar position sensor of the present invention provides improved accuracy within a given space by eliminating edge effects.

[0027] As with previous linear inductive planar position sensors, high-frequency AC carrier signals are fed into one or more oscillator coils.

[0028] According to one aspect of the invention, a linear inductive planar position sensor is formed on a substrate and includes at least one voice coil. A first sensor coil has opposite edges that extend across the opposite edges of the voice coil along a linear axis along which a linear position of a conductive object is to be detected. A second sensor coil has opposite edges that extend across opposite edges of the voice coil along the linear axis.The first and second sensor coils have geometries selected such that equal opposite magnetic fields are induced in the first and second sensor coils when a magnetic field generated by the voice coil is present and no conductive object is near the first and second sensor coils, and unequal opposite magnetic fields are induced in the first and second sensor coils when the conductive object is near the first and second sensor coils, with a difference in the unequal opposite magnetic fields induced in the first and second sensor coils correlating with the position of the conductive object.

[0029] According to one aspect of the invention, the substrate is a printed circuit board.

[0030] According to one aspect of the invention, the voice coil has the shape of a rectangle, with one long side of the rectangle being aligned in the direction of travel of the conductive measuring object to be moved.

[0031] According to one aspect of the invention, the first sensor coil is configured as a first segment having the shape of a 360° cycle of a sine function sin x starting at 0°, and a second segment having the shape of a 360° cycle of a sine function sin x starting at 0°, wherein both the first and the second segment share a common axis, wherein first ends of the first and second segments of the first sensor coil meet at a first point along the common axis and are electrically connected to each other, and second ends of the first and second segments meet at a second point along the common axis and are electrically connected to each other, the second sensor coil as a first segment having the shape of a 360° cycle of a cosine function cos x starting at 0°, and an opposite second segment having the shape of a 360° cycle of a cosine function cos x starting at 0°,The system is configured such that both the first and second segments of the second sensor coil share a common axis. The first ends of the first and second segments of the second sensor coil are electrically connected, and the second ends of the first and second segments of the second sensor coil are electrically connected. A linear position of the object being measured is detected as positions along the common axis.

[0032] According to one aspect of the invention, the at least one voice coil body is designed as a centrally tapped coil having two segments.

[0033] According to one aspect of the invention, the opposite edges of the first and second sensor coils each extend over the opposite edges of the voice coil along the linear axis by an amount selected such that an offset voltage induced at the opposite edges of the second sensor coil is canceled out in the absence of a target.

[0034] According to one aspect of the invention, a planar linear inductive position sensor system is formed on a substrate and includes at least one voice coil. A first sensor coil has opposite edges that extend across the opposite edges of the voice coil along a linear axis along which a linear position of a conductive object is to be detected. A second sensor coil has opposite edges that extend across opposite edges of the voice coil along the linear axis.The first and second sensor coils have geometries selected such that, when no conductive object is near them, equal and opposite magnetic fields are induced in the presence of a magnetic field generated by the voice coil. Unequal and opposite magnetic fields are induced when the conductive object is near the first and second sensor coils, with the difference in these opposite magnetic fields correlated with the position of the conductive object. A capacitor is coupled to the voice coil, forming an LC resonant circuit with a resonant frequency.A signal generator produces a signal at the resonant frequency, which is coupled to the oscillator coil, and sensor circuits are coupled to the first and second sensor coils.

[0035] According to one aspect of the invention, the first sensor coil is configured as a first segment having the shape of a 360° cycle of a sine function sin x, starting at 0°, and an opposing second segment having the shape of a 360° cycle of a sine function sin x, starting at 0°, wherein both the first and the second segments share a common axis, first ends of the first and second segments of the first sensor coil meet and are electrically connected, and second ends of the first and second segments meet and are electrically connected. The second sensor coil is configured as a first segment having the shape of a 360° cycle of a cosine function cos x, starting at 0°, and an opposing second segment having the shape of a 360° cycle of a cosine function cos x, starting at 0°.Both the first and second segments of the second sensor coil share a common axis. The first ends of the first and second segments of the second sensor coil are electrically connected, as are the second ends of the first and second segments of the second sensor coil. The linear position of the object being measured is recorded as positions along the common axis.

[0036] According to one aspect of the invention, a method for detecting the linear position of a conductive object relative to a substrate includes providing a voice coil on the substrate, providing a first and a second sensor coil on the substrate, wherein the first and the second sensor coil have geometries selected such that equal opposite magnetic fields are induced in the first and the second sensor coil when a magnetic field generated by the voice coil is present and no conductive object is located proximal to the first and the second sensor coil, and unequal opposite magnetic fields are induced in the first and the second sensor coil when the conductive object is located proximal to the first and the second sensor coil, and a difference in the unequal opposite magnetic fields induced in the first and second sensor coils.correlated with the position of the conductive object being measured, wherein the provided first and second sensor coils have opposite edges extending over opposite edges of the oscillating coil along a linear axis along which the linear position of the conductive object being measured is to be detected, excitation of the voice coil with a generated oscillator signal, measurement of voltages induced in the first and second sensor coils from the generated oscillator signal, and determination of the presence and position of the conductive object being measured as a function of a difference of the voltages induced in the first and second sensor coils.

[0037] According to one aspect of the invention, providing a voice coil on the substrate includes providing a resonant circuit comprising the voice coil and a capacitor, wherein the resonant circuit has a resonant frequency, and exciting the voice coil with a generated oscillator signal includes exciting the voice coil with a generated oscillator signal at the resonant frequency.

[0038] According to one aspect of the invention, providing a first and a second sensor coil on the substrate includes providing the first sensor coil, which is configured as a first segment in the form of a 360° cycle of a sine function sin x, starting at 0°, and an opposing second segment in the form of a 360° cycle of a sine function sin x, starting at 0°, wherein both the first and the second segment share a common axis. First ends of the first and second segments meet at a first point along the common axis and are electrically connected there, and second ends of the first and second segments meet at a second point along the common axis and are electrically connected there.Providing the second sensor coil, which is designed as a first segment in the form of a 360° cycle of a cosine function cos x, starting at 0°, and an opposite second segment in the form of a 360° cycle of a cosine function cos x, starting at 0°, wherein both the first and second segments of the second sensor coil share the common axis, first ends of the first and second segments of the second sensor coil are electrically connected to each other, and second ends of the first and second segments are electrically connected to each other. BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0039] The invention is explained in more detail below with reference to embodiments and the drawing, in which: Fig. 1 is a drawing showing a linear inductive planar position sensor according to the state of the art; Fig. 2 is a drawing that shows the sine sensor coil section of the linear inductive planar position sensor according to the prior art of Fig. 1 shows; Fig. 3 is a drawing that shows the cosine sensor coil section of the linear inductive planar position sensor according to the prior art of Fig. 1 shows; and Fig. 4 an amplitude-position diagram of demodulated waveforms of the linear inductive planar position sensor of Fig. Figure 1 shows the waveforms detected by the sine and cosine sensor coils; Fig. 5 is a drawing showing a linear inductive planar position sensor according to the present invention; Fig. 6 an amplitude-position diagram of demodulated waveforms of the linear inductive planar position sensor of Fig. 5 with offset compensation according to the present invention, which shows the waveforms detected by the sine and cosine sensor coils; and Fig. Figure 7 is a flowchart illustrating a process according to the present invention. DETAILED DESCRIPTION

[0040] Experts will recognize that the following description is for illustrative purposes only and is in no way limiting. Other embodiments will be readily apparent to these experts.

[0041] Now, referring to Fig. Figure 5 shows a diagram of a linear inductive planar position sensor 60 according to the present invention. The linear inductive position sensor 60 of Fig. 5 includes elements that are in the linear inductive position sensor 8 of Fig. 1. These elements are available according to the state of the art. These elements are referred to in Fig. 5 using the same reference numbers used to identify these elements in Fig. 1 can be used, although the relative geometries of these elements differ according to the principles of the present invention.

[0042] The linear inductive planar position sensor 60 from Fig. 5 includes a centrally tapped oscillator coil comprising a pair of oscillator coil segments 12 and 14. The oscillator coil is preferably rectangular in shape, with one longitudinal side of the rectangle oriented in the direction of travel of a movable conductive measuring object 20, which is to be detected by the planar inductive position sensor 60. A sine sensor coil is formed from two complementary 360° sine function segments (sin x and -sin x, both starting at 0°, where sin 0° = -sin 0° = 0) 16a and 16b, and a cosine sensor coil is formed from two complementary 360° cosine function segments (cos x and -cos x, both starting at 0°, where cos 0° = 1 and -cos 0° = -1), shown in dashed lines at reference numerals 18a and 18b. The movable measuring object 20 is formed from a conductive material and is preferably formed from a material with a relatively high electrical conductivity, such as copper or aluminum.As known in the prior art, the two oscillator coils 12 and 14, the sine sensor coil segments 16a and 16b and the cosine sensor coil segments 18a and 18b can be formed as separate layers on the multilayer substrate 10 using conventional printed circuit board manufacturing techniques.

[0043] The sine wave sensor coil is represented by lines 22 and 24, and the cosine wave sensor coil is represented by lines 26 and 28. The pair of oscillator coils 12 and 14 can be formed from a single coil having a central tap from the reference digit 30, from which it is driven, and end lines 32 and 34. The oscillator signals can be generated by a sensor interface circuit, and the sampled signals can be received and processed by a sensor interface circuit, for example, by a single integrated sensor interface circuit 36 ​​such as the LX3301A inductive sensor interface circuit available from Microsemi Corporation of Chandler, AZ.Such a sensor interface circuit 36 ​​can include a signal generator section 36a, which is used to generate the oscillator signal that is fed into one or more oscillator coils, as well as sensor circuits 36b and 36c for detecting the signals from the sine and cosine sensor coils, respectively. Capacitors 38 and 40 are each coupled between the terminals 32 and 34 of the oscillator coils 12 and 14 and ground to form LC resonant circuits. A typical value for capacitors 38 and 40 can be about 1.2 nF. The oscillator signal fed into oscillator coils 12 and 14 is preferably a sine wave, and the frequency of the oscillator signals fed into the oscillator coils depends only on the inductance of the oscillator coils and the respective capacitance values ​​of capacitors 38 and 40. A typical, non-restrictive oscillator frequency range can lie between approximately 1 MHz and approximately 6 MHz.

[0044] As with the linear inductive position sensor 8 according to the state of the art from Fig. 1 are the ends of the sine segments 16a and 16b that are closest to the end sections of the oscillator coils in the linear inductive position sensor 60 of Fig. 5 are connected at points 42 and 44. Similarly, the ends of cosine segments 18a and 18b are connected at end segments 46 and 48.

[0045] As with the linear inductive planar position sensor 8 according to the state of the art of Fig. 1 The ends of the sine sensor coil segments 16a and 16b, which are closest to the end sections of the oscillator coils, are connected to each other at points 42 and 44, and they have very few, if any, conductors of significant lengths close enough to form parallel conductors that are magnetically coupled to the conductors forming the end sections of the oscillator coils 12 and 14.

[0046] The linear inductive planar position sensor 60 from Fig. 5. The edge effect of the cosine sensor coil segments 18a and 18b, resulting from their end segments 46 and 48, which are provided to connect the opposite cosine segments 18a and 18b at their ends, also induces a voltage ΔEp / 2 at each end of the sensor. These voltages induced by the presence of the end segments 46 and 48 are compensated by canceling the additional induced voltage (Ep+ΔEp) coupled into the positive lobes of the cosine coils 18a and 18b by the oscillator coils 12 and 14. This is achieved by connecting the oscillator coils 12 and 14 as shown in Fig. Figure 5 shows that the cosine sensor coil segments are shortened by a distance d, such that their outer edges lie within the end segments 46 and 48 of the cosine sensor coil segments 18a and 18b. It should be noted that d is defined with respect to the end segments 46 and 48, and not with respect to the prior art placement. This shortening induces an additional opposite offset voltage ΔEn / 2 at each edge of the sensor. At the distance d, the magnitude of the additional opposite offset voltage ΔEn / 2 is equal to and opposite to the offset voltage ΔEp / 2 induced at the edges of the sensor when the moving target is not present. A zero-sum voltage is output at the cosine sensor coil outputs. ddt∬B0(t,x,y)dA=0 dh, (Ep+ΔEp)−(En+ΔEn)=0

[0047] The precise shortening of the oscillator coils according to the present invention depends on the geometry of the individual sensor to be compensated and must be determined for each individual case. The distance d by which the oscillator coils are shifted inwards from the edges of the cosine coils depends on many factors, including the coil geometry and the target quantity. The distance d should be adjusted for each case to compensate for the offset, since the sensor is a very complex electromagnetic structure, so there is no direct mathematical relationship between d and the geometry of the sensor. For example, for a sensor with cosine coils that have a width of 55 mm, using a measurement object with a width of 10.5 mm, a distance d of 1.24 mm compensates for the offset error.

[0048] Fig. Figure 6 is an amplitude-position diagram of demodulated waveforms of the linear inductive planar position sensor 60. Fig. 5 with offset compensation according to the present invention, showing the waveforms detected by the sine and cosine sensor coils. Waveform 62 is detected by the sine sensor coil 16a and 16b and waveform 64 by the cosine sensor coil 18a and 18b of the linear inductive planar position sensor 60 of Fig. 5 recorded. As in Fig. As can be seen in 5, there is no induced offset voltage in the demodulated cosine waveform 64 of Fig. 5.

[0049] Now, referring to Fig. Figure 7 shows a flowchart illustrating a process according to the present invention. The process begins with reference number 70.

[0050] Reference digit 72 specifies a substrate. Reference digit 74 specifies a voice coil on the substrate. Reference digits 76 and 78 specify a first and a second sensor coil on the substrate, the first and second sensor coils having geometries selected such that equal opposite magnetic fields are induced in the first and second sensor coils when a magnetic field generated by the oscillator coil is present and no conductive object is located proximal to the first and second sensor coils, and unequal opposite magnetic fields are induced in the first and second sensor coils when the conductive object is located proximal to the first and second sensor coils, with a difference in the unequal opposite magnetic fields induced in the first and second sensor coils.The position of the conductive object is correlated, with the first and second sensor coils having opposite edges extending across opposite edges of the oscillator coil along a linear axis along which the linear position of the conductive object is to be detected. Reference digit 80 indicates that the oscillator coil is excited by a generated oscillator signal. Reference digit 82 indicates that the voltages induced in the first and second sensor coils by the generated oscillator signal are measured. Reference digit 84 indicates that the presence and position of the conductive object are determined as a function of the difference between the voltages induced in the first and second sensor coils.

[0051] The procedure ends at reference number 86.

[0052] Although the embodiments and applications of this invention have been shown and described, it would be apparent to a person skilled in the art that many more modifications than those specified above are possible without deviating from the concepts of the invention. Therefore, the invention is to be considered unrestricted except with regard to the basic idea of ​​the appended claims.

Claims

[1] Planar linear inductive position sensor comprising: a substrate (10); at least one voice coil (12, 14); a first sensor coil (16a, 16b) with opposite edges extending over the opposite edges of the voice coil (12, 14) along a linear axis along which a linear position of a conductive object is to be detected; a second sensor coil (18a, 18b) with opposite edges extending along the linear axis over opposite edges of the voice coil (12, 14); wherein the first (16a, 16b) and the second (18a, 18b) sensor coils have geometries selected such that equal opposite magnetic fields are induced in the first (16a, 16b) and the second (18a, 18b) sensor coils when a magnetic field generated by the voice coil (12, 14) is present and no conductive object (20) is near the first (16a, 16b) and the second sensor coils, and unequal opposite magnetic fields are induced in the first (16a, 16b) and the second sensor coils when the conductive object (20) is near the first (16a, 16b) and the second (18a, 18b) sensor coils, wherein a difference in the unequal opposite magnetic fields induced in the first (16a, 16b) and the second (18a, 18b) sensor coils is determined by the symmetric magnetic fields of the first (16a, 16b) and the second (18a, 18b) sensor coils is determined by the symmetric magnetic fields of the first (16a, 16b) and the second (18a, 18b) sensor coils is determined by the symmetric magnetic fields of the first (16a, 16b) sensor coils. 18b) Sensor coil induced, correlated with the position of the conductive object being measured (20). [2] Planar linear inductive position sensor according to claim 1, wherein the substrate (10) is a printed circuit board. [3] Planar linear inductive position sensor according to claim 1, wherein the voice coil (12, 14) has the shape of a rectangle, wherein a long side of the rectangle is aligned in the direction of travel of the conductive measuring object (20) to be detected. [4] Planar linear inductive position sensor according to claim 1, wherein: the first sensor coil (16a, 16b) as a first segment (16a) having the shape of a 360° cycle of a sine function sin x starting at 0°, and an opposite second segment (16b) having the shape of a 360° cycle of a sine function sin x starting at 0°, wherein both the first (16a) and the second (16b) segment share a common axis, wherein first ends of the first (16a) and second (16b) segments of the first sensor coil (16a, 16b) meet and are electrically connected, and second ends of the first (16a) and second (16b) segments meet and are electrically connected; the second sensor coil (18a, 18b) is configured as a first segment (18a) having the shape of a 360° cycle of a cosine function cos x starting at 0°, and an opposite second segment (18b) having the shape of a 360° cycle of a cosine function cos x starting at 0°, wherein both the first (18a) and the second (18b) segment of the second sensor coil (18a, 18b) share the common axis, wherein first ends of the first (18a) and second (18b) segments of the second sensor coil (18a, 18b) are electrically connected to each other, and second ends of the first (18a) and second (18b) segments of the second sensor coil (18a, 18b) are electrically connected to each other; and wherein a linear position of the object being measured (20) is recorded as positions along the common axis. [5] Planar linear inductive position sensor according to claim 1, wherein the at least one voice coil (12, 14) is designed as a centrally tapped coil having two segments. [6] Planar linear inductive position sensor according to claim 1, wherein the opposite edges of the first (16a, 16b) and the second sensor coil (16a, 16b) each extend over the opposite edges of the voice coil (12, 14) along the linear axis by an amount selected to cancel a non-existent offset voltage induced at the opposite edges of the second sensor coil (18a, 18b). [7] Planar linear inductive position sensor, comprising: a substrate (10); a voice coil (12, 14); a first sensor coil (16a, 16b) with opposite edges extending over the opposite edges of the voice coil (12, 14) along a linear axis along which a linear position of a conductive object (20) is to be detected; a second sensor coil (18a, 18b) with opposite edges extending along the linear axis over opposite edges of the voice coil (12, 14); wherein the first (16a, 16b) and the second (18a, 18b) sensor coils have geometries selected such that equal opposite magnetic fields are induced in the first (16a, 16b) and the second (18a, 18b) sensor coils when a magnetic field generated by the voice coil (12, 14) is present and no conductive object (20) is near the first (16a, 16b) and the second sensor coils, and unequal opposite magnetic fields are induced in the first (16a, 16b) and the second sensor coils when the conductive object (20) is near the first (16a, 16b) and the second (18a, 18b) sensor coils. wherein a difference in the unequal opposite magnetic fields induced in the first (16a, 16b) and the second (18a, 18b) sensor coil correlates with the position of the conductive object (20); a capacitor coupled to the voice coil (12, 14) forming an LC resonant circuit with a resonant frequency; a signal generator (36a) that generates a signal at the resonant frequency, coupled to the voice coil (12, 14); and Sensor circuits coupled to the first (16a, 16b) and the second sensor coil. [8] Planar linear inductive position sensor system according to claim 7, wherein the substrate (10) is a printed circuit board. [9] Planar linear inductive position sensor system according to claim 7, wherein: the first sensor coil (16a, 16b) is configured as a first segment (16a) having the form of a 360° cycle of a sine function sin x starting at 0°, and an opposite second segment (16b) having the form of a 360° cycle of a sine function sin x starting at 0°, wherein both the first (16a) and the second (16b) segment share a common axis, first ends of the first (16a) and second (16b) segments of the first sensor coil (16a, 16b) meet and are electrically connected, and second ends of the first (16a) and second (16b) segments meet and are electrically connected; the second sensor coil (18a, 18b) is configured as a first segment (18a) having the shape of a 360° cycle of a cosine function cos x starting at 0°, and an opposite second segment (18b) having the shape of a 360° cycle of a cosine function cos x starting at 0°, wherein both the first (18a) and the second (18b) segment of the second sensor coil (18a, 18b) share the common axis, wherein first ends of the first (18a) and second (18b) segments of the second sensor coil (18a, 18b) are electrically connected to each other, and second ends of the first (18a) and second (18b) segments of the second sensor coil (18a, 18b) are electrically connected to each other; and wherein a linear position of the object being measured (20) is recorded as positions along the common axis. [10] Planar linear inductive position sensor system according to claim 7, wherein the at least one voice coil (12, 14) is designed as a centrally tapped coil. [11] Planar linear inductive position sensor system according to claim 10, wherein the capacitor coupled to the voice coil (12, 14) to form a resonant LC circuit at a resonant frequency comprises: a first capacitor (38) coupled to a first end of the centrally tapped coil; and a second capacitor (40) which is coupled to a second end of the centrally tapped coil. [12] Planar linear inductive position sensor system according to claim 7, wherein the opposite edges of the first (16a, 16b) and the second (18a, 18b) sensor coil each extend over the opposite edges of the voice coil (12, 14) along the linear axis by an amount selected to cancel a non-existent offset voltage induced at the opposite edges of the second (18a, 18b) sensor coil. [13] Method for detecting the linear position of a conductive measuring object (20) with respect to a substrate (10), comprising: Providing (74) a voice coil (12, 14) on the substrate (10); Providing (76, 78) a first (16a, 16b) and a second (18a, 18b) sensor coil on the substrate (10), wherein the first (16a, 16b) and the second sensor coil (18a, 18b) have geometries selected such that equal opposite magnetic fields are induced in the first (16a, 16b) and the second sensor coil when a magnetic field generated by the voice coil (12, 14) is present and no conductive object (20) is located proximal to the first (16a, 16b) and the second (18a, 18b) sensor coil, and unequal opposite magnetic fields are induced in the first (16a, 16b) and the second (18a, 18b) sensor coil when the conductive object (20) is located proximal to the first (16a, 16b) sensor coil. and the second (18a, 18b) sensor coil, wherein there is a difference in the unequal opposite magnetic fields induced in the first (16a, 16b) and second (18a, 18b) sensor coil,correlated with the position of the conductive object (20), wherein the provided first (16a, 16b) and second (18a, 18b) sensor coil (18a, 18b) have opposite edges extending over opposite edges of the voice coil (12, 14) along a linear axis along which the linear position of the conductive object (20) is to be detected; Excitation (80) of the voice coil (12, 14) with a generated oscillator signal; Measuring (82) the voltages induced in the first (16a, 16b) and the second (18a, 18b) sensor coil from the generated oscillator signal; and Determining (84) the presence and position of the conductive object (20) as a function of a difference in the voltages induced in the first (16a, 16b) and second (18a, 18b) sensor coil. [14] Method according to claim 13, wherein providing (74) a voice coil (12, 14) on the substrate (10) comprises providing a resonant circuit including the voice coil (12, 14) and a capacitor, wherein the resonant circuit has a resonant frequency; and wherein the excitation (80) of the voice coil (12, 14) with a generated oscillator signal includes the excitation of the voice coil (12, 14) with a generated oscillator signal at the resonant frequency. [15] Method according to claim 13, wherein providing (76, 78) a first (16a, 16b) and a second (18a, 18b) sensor coil on the substrate (10) comprises: Providing (76) the first (16a, 16b) sensor coil, which is configured as a first segment (16a) having the shape of a 360° cycle of a sine function sin x starting at 0°, and an opposing second segment (16b) having the shape of a 360° cycle of a sine function sin x starting at 0°, wherein both the first (16a) and the second (16b) segment share a common axis, first ends of the first (16a) and second (16b) segments of the first sensor coil (16a, 16b) meet and are electrically connected, and second ends of the first (16a) and second (16b) segments meet and are electrically connected; and Providing (78) the second (18a, 18b) sensor coil, which is configured as a first segment (18a) in the form of a 360° cycle of a cosine function cos x starting at 0°, and an opposing second (18b) segment in the form of a 360° cycle of a cosine function cos x starting at 0°, wherein both the first (18a) and the second (18b) segment of the second sensor coil (18a, 18b) share the common axis, first ends of the first (18a) and second (18b) segment of the second sensor coil (18a, 18b) are electrically connected to each other, and second ends of the first (18a) and second (18b) segment are electrically connected to each other.

Images