CN112902817A - Magnetic linear position sensor - Google Patents

Magnetic linear position sensor Download PDF

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CN112902817A
CN112902817A CN202110170879.4A CN202110170879A CN112902817A CN 112902817 A CN112902817 A CN 112902817A CN 202110170879 A CN202110170879 A CN 202110170879A CN 112902817 A CN112902817 A CN 112902817A
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CN112902817B (en
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陈兆麟
陈秉男
陈圣文
杨仁昌
黄纯摇
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Kita Sensor Tech Co Ltd
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/003Measuring arrangements characterised by the use of electric or magnetic techniques for measuring position, not involving coordinate determination
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness

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Abstract

The invention provides a magnetic linear position sensor, which is used for detecting the position of a magnet reciprocating along a linear stroke, wherein a magnetic angle type sensing element is arranged at one side of the linear stroke to sense the magnetic field of the magnet and output a sine signal and a cosine signal, and a processing unit digitalizes the sine signal and the cosine signal into a sine signal value and a cosine signal value, and then atan2 (subtracting the sine signal value of a first preset value/subtracting the cosine signal value of a second preset value) is operated to obtain a curvature value; the processing unit inputs the curvature value into a mathematical model fitting a characteristic curve of the magnetic angle type sensing element to obtain a relative distance between the magnetic angle type sensing element and the magnet. Therefore, the detection distance of the magnetic angle type sensing element can be increased, and the using number of the magnetic angle type sensing element is further reduced.

Description

Magnetic linear position sensor
Technical Field
The present invention relates to position sensors, and more particularly to a magnetic linear position sensor.
Background
Referring to fig. 1, one conventional way to obtain the detection distance of a magnetic angle type sensing element S (e.g., AMR, Hall, TMR …) is to make the magnetic angle type sensing element S sense the magnetic field of a magnet M moving along a linear stroke P1, so as to generate a sine wave signal and a cosine wave signal related to a moving distance of the magnet M and output them to a signal processor 10, the signal processor 10 digitizes the sine wave signal and the cosine wave signal into a digitized sine wave signal sin formed of a plurality of sine signal values Usin as shown in fig. 1 and a digitized cosine wave signal cos formed of a plurality of cosine signal values Ucos as shown in fig. 1, and performs a second derivative (atan2) operation of an ARCTAN function (ARCTAN) on the sine signal values Usin and the cosine signal values Ucos, i.e., atan2(Usin/Ucos), to obtain a plurality of curvature values, and the curvature values form a curvature curve C1 as shown in fig. 1, the curvature value of each point on a valid line segment L1 in the curvature curve C1 corresponds to a detection distance, and since the curvature value of the valid line segment L1 only ranges from 0.2 to 1.2, it means that an effective detection distance of the magnetic angle sensor S is not long, for example, the detection distance shown in fig. 1 is only 6mm, and therefore, assuming that the length to be detected is 6 times of 6mm, at least 6 magnetic angle sensors S need to be arranged in parallel for detection at the same time.
Disclosure of Invention
The present invention is directed to a magnetic linear position sensor, which can increase the detection distance of a magnetic angle sensor therein, thereby reducing the number of magnetic angle sensors.
The invention provides a magnetic linear position sensor, which is used for detecting the position of a magnet reciprocating along a linear stroke and comprises a magnetic angle type sensing element and a processing unit; the magnetic angle type sensing element is arranged on one side of the linear stroke to sense the magnetic field of the magnet and output a sine signal and a cosine signal; the processing unit is electrically connected with the magnetic angle type sensing element to receive the sine signal and the cosine signal, digitize the sine signal and the cosine signal into a sine signal value and a cosine signal value, and subtracts a first preset value from the sine signal value and the cosine signal valuePerforming a second derivative operation of an arctan function between the signal value and the cosine signal value subtracted by a second predetermined value, i.e., atan2 (subtracting the sine signal value of the first predetermined value/subtracting the cosine signal value of the second predetermined value) to obtain a curvature value; the processing unit inputs the curvature value into a mathematical model related to the characteristics of the magnetic angle type sensing element to obtain a relative distance between the magnetic angle type sensing element and the magnet; the mathematical model is formed by a polynomial equation
Figure BDA0002938891480000021
And a curvature value range configured to fit a characteristic curve of the magnetic angle type sensing element, wherein i is equal to 1,2,3 … n, yiIs the relative distance, xiIs the curvature value, beta0~βmIs the coefficient of the magnetic angle-type inductive element, and the minimum and maximum values of the curvature value range are the curvature values at both ends of the characteristic curve.
In some embodiments of the present invention, the mathematical model is established in a calibration procedure of the magnetic linear position sensor, in which the magnet moves along the linear stroke, a signal processing device enables the processing unit to request the magnetic angle type sensing element to transmit back the currently generated sine signal and the cosine signal at a sampling frequency until the magnet has finished the linear stroke; the processing unit digitizes the sine signal and the cosine signal and outputs the signals to the signal processing device, the signal processing device obtains the corresponding relation between the position of each sampling point of the magnet in the linear stroke and the digitized sine signal value and cosine signal value according to the length of the linear stroke and the sampling frequency, the signal processing device subtracts a first preset value from the sine signal value and subtracts a second preset value from the cosine signal value, the signal processing device performs the second derivative (atan2) operation of the arctan function on the sine signal value subtracted by the first preset value and the cosine signal value subtracted by the second preset value, namely atan2 (subtracts the sine signal value of the first preset value/subtracts the cosine signal value of the second preset value), and obtains the relative sine signal value and the cosine signal value subtracted by the first preset valueThe signal processing device uses an effective line segment in the curvature curve as the characteristic curve of the magnetic angle type sensing element, determines an effective detection distance and a corresponding curvature value range of the magnetic angle type sensing element according to the characteristic curve, and determines the polynomial equation by curve fitting and linear regression analysis
Figure BDA0002938891480000022
M and beta of0~βmAnd the signal processing device writes the polynomial equation and the curvature value range into the processing unit as the mathematical model of the characteristic curve.
In some embodiments of the present invention, the first predetermined value is one of a maximum value and a minimum value of the sinusoidal signal values; the second predetermined value is one of two of the combinations of the maximum value and the minimum value of the cosine signal values.
In some embodiments of the invention, m is 6.
In some embodiments of the present invention, the magnetic angle sensing element has two magnetoresistive bridges 45 ° apart, wherein one of the magnetoresistive bridges senses the magnetic field of the magnet and generates a sine wave signal, and wherein the other magnetoresistive bridge senses the magnetic field of the magnet and generates a cosine wave signal 45 ° apart from the sine wave signal.
In some embodiments of the invention, the processing unit inputs the curvature value into the mathematical model only if the curvature value is determined to be within the range of curvature values.
The invention has the beneficial effects that: the processing unit only needs to digitize the sine signal and the cosine signal transmitted by the magnetic angle type sensing element, and then carries out atan2 (subtracting the sine signal value of the first preset value/subtracting the cosine signal value of the second preset value) operation on the sine signal value subtracted by the first preset value and the cosine signal value subtracted by the second preset value to obtain a curvature value, and then inputs the curvature value into the mathematical model, thus quickly obtaining a relative distance between the magnetic angle type sensing element and the magnet by a simple unary m-degree polynomial equation; and the characteristic curve fitted by the mathematical model determines an effective detection distance of the magnetic angle type sensing element and a corresponding curvature value range, and in the correction procedure, the effective detection distance can be increased by properly translating the sine signal values and the cosine signals obtained by the magnetic angle type sensing element and then performing second derivative (atan2) operation of an ARCTAN function (ARCTAN), thereby reducing the number of magnetic angle type sensing elements and increasing the detection distance of the magnetic linear position sensor.
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Fig. 1 illustrates a conventional method for obtaining the detection distance of a magnetic angle sensor.
FIG. 2 illustrates the components and applications involved in one embodiment of the magnetic linear position sensor of the present invention.
Fig. 3 is a detailed circuit diagram included in the magnetic angle sensor of the present embodiment.
Fig. 4 is a schematic waveform diagram of the digitized sine wave signal sin and the digitized cosine wave signal cos digitized by the processing unit of the present embodiment.
Fig. 5 illustrates the digitized sine wave signal sin and the digitized cosine wave signal cos of fig. 4 shifted down by a first preset value and a second preset value, respectively.
Fig. 6 illustrates the second derivative of the ARCTAN function (atan2) of the sine wave signal sin 'and the cosine wave signal cos' shown in fig. 5 to obtain a plurality of corresponding curvature values, which constitute a curvature curve C2.
Fig. 7 illustrates that the X-axis data and the Y-axis data of the effective line segment L2 of the curvature curve C2 shown in fig. 6 are replaced with each other to become a replaced effective line segment L2'.
Detailed Description
The invention is described in detail below with reference to the following figures and examples:
before the present invention is described in detail, it should be noted that in the following description, like elements are represented by like reference numerals.
Referring to fig. 2, an embodiment of the magnetic linear position sensor of the present invention is used to detect the position of a magnet M reciprocating along a linear stroke P2, for example, the magnet M is a piston disposed in a cylinder 1, and the linear stroke P2 is the piston stroke of the piston reciprocating in the cylinder 1; the magnetic linear position sensor 2 of the present embodiment mainly includes a magnetic angle sensor 21 and a processing unit 22, such as a microprocessor or a Micro Controller Unit (MCU). The magnetic angle type sensing element 21 is disposed at one side of the linear stroke P2, for example, an outer wall surface of the cylinder 1, to sense the magnetic field of the magnet M and output an analog sine signal and a cosine signal; the processing unit 22 is electrically connected to the magnetic angle sensor 21 for receiving the sine signal and the cosine signal, and a mathematical model related to the characteristics of the magnetic angle sensor 21 is stored in the processing unit 22 and is represented by a polynomial equation
Figure BDA0002938891480000041
And a curvature value range configured to fit a characteristic curve of the magnetic angle-type sensing element 21, wherein i is 1,2,3 … n, yiRepresents a relative distance, x, between the magnetic angle type sensing element 21 and the magnet MiRepresents a curvature value, beta0~βmRepresenting the coefficients of the magnetic angle-type inductive element 21, the minimum and maximum values of the curvature value range are the curvature values at both ends of the characteristic curve.
Specifically, the mathematical model is established in a calibration procedure of the magnetic linear position sensor 2, and since the characteristics of the magnetic angle-type sensing element 21 in each magnetic linear position sensor 2 are different, the magnetic linear position sensor 2 needs to be calibrated to find the mathematical model corresponding to the characteristics of the magnetic angle-type sensing element 21 before the magnetic linear position sensor 2 is shipped; and as shown in fig. 3, the magnetic angle type sensing element 21 (e.g., AMR, Hall, TMR …) has two magnetoresistive bridges (bridges) 211, 212 with a phase difference of 45 ° (i.e., a 45 ° angle is sandwiched); in the calibration process, as shown in fig. 2, the magnet M is moved from the end of the linear stroke P2 away from the magnetic angle-type sensing element 21 to the magnetic angle-type sensing element 21, and after passing through the magnetic angle-type sensing element 21, the magnet M is moved to the other end of the linear stroke P2 away from the magnetic angle-type sensing element 21, in the process, the two magnetoresistive bridges 211 and 212 continuously sense the magnetic field of the magnet M to generate a sine wave signal SIN and a cosine wave signal COS with a phase difference of 45 °.
Meanwhile, a signal processing device 3, such as but not limited to a personal computer, enables the processing unit 22 to request the magnetic angle sensor 21 to transmit back the sine signal (i.e. the value of a certain point of the sine wave signal SIN, the analog voltage value) and the cosine signal (i.e. the value of a certain point of the cosine wave signal COS, the analog voltage value) generated at present at a sampling frequency (e.g. 10 times/second) until the magnet M has finished the linear stroke P2, so that the magnetic angle sensor 21 transmits back 10 sine signals and 10 cosine signals to the processing unit 22 every second, and the processing unit 22 digitizes and outputs the received sine signals and cosine signals to the signal processing device 3. The digitized values of the sine signal values Usin and the cosine signal values Ucos may be compared to the values indicated by the left vertical axis of fig. 4.
Therefore, the signal processing device 3 can obtain the corresponding relationship between the position of the magnet M at each sampling point in the linear stroke P2 and the digitized sine signal values Usin and the digitized cosine signal values Ucos, such as the digitized sine signal sin composed of the digitized sine signal values Usin shown in fig. 4 and the digitized cosine signal cos composed of the digitized cosine signal values Ucos shown in fig. 4, according to the moving distance of the magnet M (i.e. the length of the linear stroke P2) and the sampling frequency.
Then, the signal processing device 3 subtracts a first preset value from the sine signal values Usin to obtain Usin ', which is equivalent to shift down (offset) the digitized sine wave signal sin by the first preset value to obtain a shifted digitized sine wave signal sin' as shown in fig. 5, and the signal processing device 3 subtracts a second preset value from the cosine signal values Ucos to obtain Ucos ', which is equivalent to shift down (offset) the digitized cosine wave signal cos by the second preset value to obtain a shifted digitized cosine wave signal cos' as shown in fig. 5; in this embodiment, the first predetermined value is one half of a sum of a maximum value and a minimum value of the plurality of sinusoidal signal values Usin, but not limited thereto; the second predetermined value is one half of a sum of a maximum value and a minimum value of the plurality of cosine signal values Ucos, but not limited thereto.
Then, the signal processing device 3 performs a second derivative (atan2) operation of an ARCTAN function (ARCTAN) on the sine signal values Usin '(i.e. the translated digitized sine wave signal sin') subtracted by the first predetermined value and the cosine signal values Ucos '(i.e. the translated digitized cosine wave signal cos') subtracted by the second predetermined value, i.e. atan2(Usin '/Ucos'), to obtain corresponding curvature values, which can be compared with the values indicated by the right vertical axis of fig. 6, and which form a curvature curve C2 as shown in fig. 6, and an effective segment L2 of the curvature curve C2 represents the characteristic curve of the magnetic angle type sensing element 21 and determines an effective detection distance of the magnetic angle type sensing element 21 and the corresponding curvature value range, for example, when the curvature value is-1, the distance value is-2 mm from the effective segment L2 (the characteristic curve), referring to fig. 2, it may represent that the magnet M is located at the left side of the magnetic angle type sensing element 21 and is spaced apart from the magnetic angle type sensing element 21 by about 2 mm; similarly, when the curvature value is 2, it can be known that the distance value is 2.6mm, which represents that the magnet M is located at the right side of the magnetic angle type sensing element 21 and is about 2.6mm away from the magnetic angle type sensing element 21; as shown in fig. 6, in the present embodiment, since the curvature value range can reach-pi, the corresponding effective detection distance can be increased to 14mm, and thus, in the present embodiment, after the signal value obtained by the magnetic angle type sensing element 21 is translated, the second derivative (atan2) of the ARCTAN function (ARCTAN) is calculated, and the detection distance (14mm) of the magnetic angle type sensing element 21 can be increased to more than twice of the known technique (6mm), so that, assuming that the required detection length is 6 times of 6mm, only 3 magnetic angle type sensing elements 21 need to be arranged in parallel for simultaneous detection, and the number of the magnetic angle type sensing elements 21 can be reduced.
Then, the signal processing device 3 uses the valid line segment L2 (i.e. the valid detection distance and the corresponding curvature value range) as the characteristic curve of the magnetic angle sensor 21 and determines the valid detection distance of the magnetic angle sensor 21 and the corresponding curvature value range, and the signal processing device 3 determines the polynomial equation by curve fitting and linear regression analysis according to the valid detection distance and the curvature value range
Figure BDA0002938891480000071
M and beta of0~βmThe value of (c).
Specifically, as shown in fig. 7 (a), if the effective line segment L2 is composed of 100 curvature values (the curvature value range) corresponding to 100 positions (i.e., the distance values between the 100 magnets M and the magnetic angle sensor 21, i.e., the effective detection distance), in the present embodiment, the signal processing device 3 first replaces the data of the X axis and the Y axis of the effective line segment L2, so that the X axis shows the curvature values and the Y axis shows the corresponding distance values, and the effective line segment L2 becomes the replaced effective line segment L2', as shown in fig. 7 (B). Then, the signal processing device 3 determines a polynomial equation most suitable for the replaced effective line segment L2
Figure BDA0002938891480000072
For example, by using Polynomial Fitting (Polynomial Fitting), regression equation using univariate m-degree Polynomial
Figure BDA0002938891480000073
The permuted valid line segment L2' is fitted and the polynomial regression equation is solved with a matrix as shown below:
Figure BDA0002938891480000074
wherein i is 1,2,3 … n, y1~ynRepresents the 100 distance values, x1~xnRepresents the 100 curvature values, beta0~βmIs a coefficient, and since the characteristics of each of the magnetic angle type induction elements 21 are different, the coefficient β thereof0~βmSo that the coefficients β of the magnetic angle-type inductive element 21 can be found by the matrix operation0~βmAnd a polynomial equation that determines the fit to be used for the displaced valid line segment L2'. For example, the embodiment may use the polyfit instruction provided by MATLAB to find the best parameters of the unary mth degree polynomial equation and the equation that best fits the replaced valid line segment L2'.
For example, the above-mentioned known 100 curvature value (x) is indicated by the polyfit instruction1~xn) Corresponding to the 100 distance values (y)1~yn) The signal processing apparatus 3 employs a univariate 6-degree polynomial equation having the best fitting result, for example, y 2.4431x, which is substituted into 8-degree polynomial equations of 1-8, respectively, and when the optimal coefficients of the 8-degree polynomial equations and the fitting result of the optimal coefficients with the replaced effective line segment L2 'are found, and the result of fitting the univariate 6-degree polynomial equation to the replaced effective line segment L2' is found to be optimal from the 8-degree polynomial equations6-8.2418x5+15.967x4-10.349x3+7.6091x2+1.567x +1.0009, and taking the unary 6 th-order polynomial equation as the mathematical model; wherein y represents a distance value between the magnet M and the magnetic angle type inductive element 21, and x represents a curvature value. Then, the signal processing apparatus 3 writes the unary 6 th-order polynomial equation and the curvature value range into the processing unit 22 as the mathematical model, thereby completing the calibration procedure.
Thereby, when the magnetic linear position sensor 2 is practically applied to, for example, the cylinder 1 shown in fig. 2, and the processing unit 22 receives the analog sine signal and the cosine signal transmitted from the magnetic angle type sensing element 21, the processing unit 22 digitizes the sine signal and the cosine signal into a sine signal value and a cosine signal value, and after subtracting the first preset value from the sine signal value and subtracting the second preset value from the cosine signal value, performs second derivative (atan2) operation of an ARCTAN function (ARCTAN) on the sine signal value subtracted by the first preset value and the cosine signal value subtracted by the second preset value, that is, atan2 (subtracting the sine signal value by the first preset value/subtracting the cosine signal value by the second preset value) to obtain a curvature value; then, when the processing unit 22 determines that the curvature value is within the curvature value range, the processing unit substitutes the curvature value into the mathematical model, so as to obtain a distance value by using the 6 th-order polynomial equation, where the distance value represents a relative distance between the magnetic angle type sensing element 21 and the magnet M; then, the processing unit 22 can directly output the distance value for the back-end application, or convert the distance value into a corresponding analog signal, such as an analog voltage (e.g., a voltage value of 1-5V) or an analog current (e.g., a current value of 4-20 mA), and output the analog voltage or the analog current to the back-end application.
To sum up, the above embodiment uses the mathematical model in the processing unit to fit the characteristic curve of the magnetic angle sensor 21, and the processing unit only needs to digitize the sine signal and the cosine signal transmitted from the magnetic angle sensor 21, then performs atan2 (subtracting the sine signal value of the first preset value/subtracting the cosine signal value of the second preset value) operation on the sine signal value subtracted by the first preset value and the cosine signal value subtracted by the second preset value to obtain a corresponding curvature value, and then inputs the curvature value into the mathematical model for calculating the distance, i.e. a relative distance between the magnetic angle sensor 21 and the magnet M can be quickly obtained by a simple unitary M-degree polynomial equation; in addition, the characteristic curve fitted by the mathematical model determines an effective detection distance of the magnetic angle sensor 21 and a corresponding curvature value range, and in the present embodiment, in the calibration procedure, the effective detection distance can be increased by properly translating the sine signal values and the cosine signals obtained by the magnetic angle sensor 21 and then performing the second derivative (atan2) operation of the ARCTAN function (ARCTAN), so as to achieve the effects and purposes of reducing the number of the magnetic angle sensor 21 and increasing the detection distance of the magnetic linear position sensor 2.
The above description is only for the preferred embodiment of the present invention, and it is not intended to limit the scope of the present invention, and any person skilled in the art can make further modifications and variations without departing from the spirit and scope of the present invention, therefore, the scope of the present invention should be determined by the claims of the present application.

Claims (7)

1. A magnetic linear position sensor for sensing the position of a magnet reciprocating along a linear path, comprising:
a magnetic angle type induction element provided at one side of the linear stroke to induce the magnetic field of the magnet and output a sine signal and a cosine signal; and
the processing unit is electrically connected with the magnetic angle type induction element to receive the sine signal and the cosine signal, digitize the sine signal and the cosine signal into a sine signal value and a cosine signal value, and performs second derivative operation of an arc tangent function on the sine signal value subtracted by a first preset value and the cosine signal value subtracted by a second preset value to obtain a curvature value; the processing unit inputs the curvature value into a mathematical model related to the characteristics of the magnetic angle type sensing element so as to obtain the relative distance between the magnetic angle type sensing element and the magnet; the mathematical model is formed by polynomial equations
Figure FDA0002938891470000011
And a curvature value range constructed to fit a characteristic curve of the magnetic angle type sensing element, wherein i is 1,2,3 … n, yiRepresents the relative distance, xiRepresents the curvature value, beta0~βmIs a coefficient of the magnetic angle type induction element, the curveThe minimum and maximum values of the range of values of the rate are the values of curvature at the ends of the characteristic curve.
2. The magnetic linear position sensor according to claim 1, wherein the mathematical model is established in a calibration procedure of the magnetic linear position sensor in which the magnet moves along the linear stroke, the signal processing device causes the processing unit to request the magnetic angle type sensing element to transmit back the currently generated sine signal and the cosine signal at a sampling frequency until the magnet has completed the linear stroke; the processing unit digitizes the sine signal and the cosine signal and outputs the signals to the signal processing device, the signal processing device obtains the corresponding relation between the position of each sampling point of the magnet in the linear stroke and the digitized sine signal value and cosine signal value according to the length of the linear stroke and the sampling frequency, the signal processing device subtracts the first preset value from the sine signal value and subtracts the second preset value from the cosine signal value, the signal processing device performs the second derivative operation of the arctan function on the sine signal value subtracted by the first preset value and the cosine signal value subtracted by the second preset value to obtain a plurality of corresponding curvature values, the curvature values form a curvature curve, and the signal processing device takes the effective line segment in the curvature curve as the characteristic curve of the magnetic angle type sensing element, determining the effective detection distance of the magnetic angle type induction element and the corresponding curvature value range according to the characteristic curve, and determining the m value and beta value of the polynomial equation by curve fitting and linear regression analysis0~βmAnd the signal processing device writes the polynomial equation and the curvature value range into the processing unit as the mathematical model of the characteristic curve.
3. The magnetic linear position sensor of claim 2 wherein the first predetermined value is one-half of the sum of the maximum and minimum values of the sinusoidal signal values; the second predetermined value is one-half of the sum of the maximum value and the minimum value in the cosine signal value.
4. The magnetic linear position sensor of any of claims 1 to 3, wherein m is 6.
5. The magnetic linear position sensor according to any of claims 1 to 3, wherein the magnetic angle type sensing element has two magnetoresistive bridges which are 45 ° apart, one of the two magnetoresistive bridges sensing the magnetic field of the magnet and generating a sine wave signal, and the other magnetoresistive bridge sensing the magnetic field of the magnet and generating a cosine wave signal which is 45 ° apart from the sine wave signal.
6. The magnetic linear position sensor of any of claims 1 to 3, wherein the curvature value ranges from- π to π.
7. The magnetic linear position sensor according to any of claims 1 to 3, wherein the processing unit inputs the curvature value into the mathematical model only if the curvature value is determined to be within the curvature value range.
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