Linear position sensor

Abstract

The invention discloses a linear position sensor, and belongs to the technical field of magnetic sensors, the linear position sensor comprises a sensing element group, the sensing element group is formed by arranging a plurality of sensing elements at a fixed pitch, and each sensing element is composed of a plurality of magnetic resistance units in a curve line shape; the linear position sensor is used in cooperation with a magnetic railing ruler with a specific magnetic pole length, and the magnetic railing ruler forms periodic magnetic field distribution through N-pole and S-pole magnetic poles which are arranged at equal intervals. On the basis, the widths of the magnetic resistance units are adjusted according to different distances between the magnetic resistance units and the magnetic railing ruler, so that the magnetic hysteresis is remarkably reduced, and the repeated positioning precision is improved; when the sensing elements and the magnetic railing ruler perform relative linear motion, the magnetic resistance unit induces magnetic field changes, the sensing elements form two Wheatstone bridges through combination, respectively sense magnetic field angle distribution, convert magnetic resistance changes into electric signals and output two orthogonal sinusoidal signals and cosine signals, and then the magnetic railing ruler is determined according to the two signals. And calculating a corresponding straight line position.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic sensors, and specifically to a linear position sensor. Background Art

[0002] A linear position sensor is a sensor used to measure the position of linear motion, and is widely used in fields such as linear motors, machine tools, medical equipment, and industrial automation, providing accurate position information for the detection and control of linear motion positions.

[0003] Currently, the linear position sensors used in the market usually cooperate with a magnetic scale with a specific pole length and alternately magnetized N / S poles. This cooperation method enables the sensor to sense the periodic magnetic field changes on the magnetic scale bar and calculate the corresponding linear position. In terms of the induction principle, linear position sensors are mainly based on the Hall induction principle and the magnetoresistive induction principle. However, due to the low sensitivity and low signal-to-noise ratio of the Hall effect sensor itself, the final position accuracy and resolution are not high enough, and the repeat positioning accuracy is also relatively low, making it difficult to meet the strict requirements of the high-end application market. In contrast, magnetoresistive effect sensors have at least an order of magnitude improvement in terms of sensitivity and signal-to-noise ratio. However, the ferromagnetic thin film used in the linear position sensor based on the magnetoresistive principle has certain hysteresis problems, which will lead to a decrease in the repeat positioning accuracy of the sensor. Therefore, for the linear position sensor based on the magnetoresistive principle, how to effectively reduce the hysteresis of the ferromagnetic thin film has become the key to improving its repeat positioning accuracy. Summary of the Invention

[0004] The purpose of the present invention is to provide a linear position sensor to solve the problems raised in the above background art.

[0005] To solve the above technical problems, the present invention provides the following technical solution: A linear position sensor includes a sensing element group; the sensing element group is composed of a plurality of sensing elements arranged at a fixed pitch, and each sensing element is composed of a number of magnetoresistive units in the shape of curved lines. Further, the linear position sensor is used in cooperation with a magnetic scale, and the magnetic scale is formed by alternately magnetizing N and S poles with a specific pole length; the specific pole length is the length of a single N or S pole, and is repeated on the magnetic scale with the length of a single pole as a period to form a periodic magnetic field distribution. Further, the magnetoresistive unit is selected from one of the three types of anisotropic magnetoresistance AMR, giant magnetoresistance GMR, and tunneling magnetoresistance TMR, and is formed into a curved line shape by etching a magnetoresistive thin film. Further, each sensing element includes I magnetoresistive units. For the i-th magnetoresistive unit, i = 1, 2,..., I; the distance between the i-th magnetoresistive unit and the magnetic scale is r. i, when the spacing increases, the width of the corresponding magnetoresistive element also increases accordingly; Furthermore, the specific pole length is set as p, and the fixed pitch D between the sensing elements is set according to the pole length and the type of magnetoresistive element: when the magnetoresistive element is anisotropic magnetoresistive (AMR), the fixed pitch is set as p / 4; when the magnetoresistive element is giant magnetoresistive (GMR) and tunneling magnetoresistive (TMR), the fixed pitch is set as p / 2.

[0006] Furthermore, the sensing element groups are combined to form two Wheatstone bridges; the two Wheatstone bridges sense the magnetic field angle distribution of the magnetic scale respectively. When there is a relative linear motion between the sensing elements and the magnetic scale, the magnetoresistive elements in the sensing elements sense the periodic magnetic field change on the surface of the magnetic scale, and convert the magnetoresistance change in the magnetoresistive elements into electrical signals through the two Wheatstone bridges, and output two orthogonal sine signals Usin and cosine signals Ucos respectively. According to the formula, the corresponding linear position X is calculated, and the calculation formula is: X = atan2(Ucos, Usin) × [p / (2×π)].

[0007] Compared with the prior art, the beneficial effects achieved by the present invention are: By adopting a plurality of groups of sensing elements arranged at a fixed pitch and composed of magnetoresistive elements in the shape of curved lines, the present invention cooperates with a magnetic scale with a specific pole length, and combines two Wheatstone bridges to realize the sensing of the magnetic field angle, and further realizes the precise sensing of the linear position; in this process, by using the magnetoresistive elements in the shape of curved lines and adjusting the width of the magnetoresistive elements according to the different distances between them and the magnetic scale, the hysteresis can be significantly reduced, the repeat positioning accuracy can be improved, and the application requirements of high position accuracy and high resolution can be met at the same time. Description of the Drawings

[0008] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the drawings: Figure 1 is a schematic structural diagram of a linear position sensor cooperating with a magnetic scale; Figure 2 is a schematic structural diagram of several groups of sensing elements of a linear position sensor; Figure 3 is a schematic diagram of the output signal of a linear position sensor and the calculation of the linear position; Figure 4 is a schematic structural diagram of several magnetoresistive elements of each sensing element in a linear position sensor; Figure 5 is a schematic diagram of the width change of several magnetoresistive elements of each sensing element in a linear position sensor; Figure 6 It is a schematic diagram for comparing the repeat positioning accuracy of a linear position sensor; In the figure: 10: Linear position sensor; 20: Magnetic scale; 101: First sensing element; 102: Second sensing element; 103: Third sensing element; 104: Fourth sensing element; 105: Fifth sensing element; 106: Sixth sensing element; 107: Seventh sensing element; 108: Eighth sensing element. Specific implementation mode

[0009] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0010] Please refer to Figures 1-6 , the present invention provides a technical solution: a linear position sensor. The linear position sensor 10 includes a sensing element group, which is composed of a plurality of sensing elements arranged at a fixed pitch D, and each sensing element is composed of several magnetoresistive units in the shape of curved lines; the magnetoresistive unit is selected from one of the three types of anisotropic magnetoresistance AMR, giant magnetoresistance GMR, and tunneling magnetoresistance TMR, and is formed into a curved line shape by etching a magnetoresistive thin film; The linear position sensor 10 is used in cooperation with the magnetic scale 20. The magnetic scale 20 is formed with N poles and S poles by alternately magnetizing magnetic poles with a specific magnetic pole length; the specific magnetic pole length is the length of a single N pole or S pole, and is repeatedly arranged on the magnetic scale 20 at a fixed length of a single magnetic pole to form a periodic magnetic field distribution; the specific magnetic pole length is set to p, and the fixed pitch D between the sensing elements is set to p / 2 or p / 4 according to the magnetic pole length p: When the magnetoresistive unit of the sensing element is selected as anisotropic magnetoresistance AMR, considering that AMR can only determine the magnetic field angle or position inside a single magnetic pole in the saturation state, the fixed pitch D between the sensing elements is set to p / 4; when the magnetoresistive unit of the sensing element is selected as giant magnetoresistance GMR or tunneling magnetoresistance TMR, GMR and TMR can determine the magnetic field angle or position inside a pair of magnetic poles (including N poles and S poles), so the fixed pitch D between the sensing elements is set to p / 2; Each sensing element includes I magnetoresistive units. For the i-th magnetoresistive unit, i = 1, 2,..., I; the distance between the i-th magnetoresistive unit and the magnetic scale 20 is r i , when the distance increases, the width of the corresponding magnetoresistive unit also increases; The sensing element group includes a first sensing element 101, a second sensing element 102, a third sensing element 103, a fourth sensing element 104, a fifth sensing element 105, a sixth sensing element 106, a seventh sensing element 107, and an eighth sensing element 108; the two Wheatstone bridges include a first Wheatstone bridge and a second Wheatstone bridge; the first Wheatstone bridge includes the first sensing element 101, the third sensing element 103, the fifth sensing element 105, and the seventh sensing element 107; the midpoint of the connection between the first sensing element 101 and the third sensing element 103 serves as the positive output terminal of the cosine signal Ucos; the midpoint of the connection between the seventh sensing element 107 and the fifth sensing element 105 serves as the negative output terminal of the cosine signal Ucos; the second Wheatstone bridge includes the second sensing element 102, the fourth sensing element 104, the sixth sensing element 106, and the eighth sensing element 108; the midpoint of the connection between the second sensing element 102 and the fourth sensing element 104 serves as the positive output terminal of the sine signal Usin; the midpoint of the connection between the eighth sensing element 108 and the sixth sensing element 106 serves as the negative output terminal of the sine signal Usin; the cosine signal Ucos output by the first Wheatstone bridge and the sine signal Usin output by the second Wheatstone bridge have a phase difference of 90°, forming a pair of orthogonal signals; The sensing element group of the linear position sensor 10 forms two Wheatstone bridges by combining multiple sensing elements, respectively sensing the magnetic field angle distribution of the magnetic scale 20. When there is a relative linear motion between the sensing elements and the magnetic scale 20, the magnetoresistive units in the sensing elements sense the periodic magnetic field changes on the surface of the magnetic scale 20, and convert the magnetoresistance changes in the magnetoresistive units into electrical signals through the two Wheatstone bridges, respectively outputting two orthogonal sine signals Usin and cosine signals Ucos; according to the two signals, the corresponding linear position is calculated, such as Figure 3 shown, according to the output signals, the corresponding linear position X is calculated: X = atan2(Ucos, Usin) × [p / (2 × π)]; in order to eliminate the influence of different magnetic pole lengths on the position data, the calculated linear position X is normalized: divide X by the magnetic pole length p, that is, X / P; Embodiment: As Figure 1 shown, a linear sensor 10 and a magnetic scale 20, the linear position sensor 10 is used in cooperation with a magnetic scale 20 with a specific magnetic pole length alternately magnetized with N / S. The magnetic scale 20 generates an alternately changing magnetic field distribution. The linear position sensor 10 is located above the magnetic scale 20 to sense the alternately changing magnetic field; the specific magnetic pole length of the magnetic scale is the length of a single N pole or a single S pole, and they are alternately arranged to form the magnetic field distribution of the magnetic scale, and the specific magnetic pole length is set as p; As Figure 2As shown, a linear position sensor 10 includes a group of sensing elements: a first sensing element 101, a second sensing element 102, a third sensing element 103, a fourth sensing element 104, a fifth sensing element 105, a sixth sensing element 106, a seventh sensing element 107, and an eighth sensing element 108. These sensing elements are neatly arranged on the sensor body at a fixed pitch D to form a sensing element array. The fixed pitch D is related to the specific pole length p of the used magnetic scale 20. In this embodiment, according to the type of the employed magnetoresistive unit, the fixed pitch D is set to p / 2 or p / 4. Each sensing element is composed of a number of magnetoresistive units in the shape of curved lines, and these magnetoresistive units can be one type of anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), or tunneling magnetoresistance (TMR). As Figure 4 shown in (a) and (b) thereof, the magnetoresistive units are etched into the shape of curved lines, including but not limited to shapes such as arc-shaped and wavy. (a) shows the wavy magnetoresistive units, and (b) shows the arc-shaped magnetoresistive units. This design can significantly reduce the shape anisotropy field of the magnetoresistive units, thereby reducing the hysteresis of the entire linear position sensor and improving the repeat positioning accuracy. The widths of a number of magnetoresistive units gradually increase as the distance between the magnetoresistive units and the magnetic scale increases. As Figure 5 shown, the sensing element is composed of 7 magnetoresistive units. As the distance between the magnetoresistive units and the magnetic scale gradually increases from r1 to r7, the widths of the magnetoresistive units also gradually increase from w1 to w7 in sequence. As the distance between the magnetoresistive units and the magnetic scale increases, the magnetic field intensity of the magnetic scale sensed by the magnetoresistive units decreases in the order of 1 / r 3 magnitude, and the corresponding hysteresis will also increase accordingly. Therefore, gradually increasing the width of the magnetoresistive units as the distance between the magnetoresistive units and the magnetic scale increases can further gradually reduce the shape anisotropy field of the magnetoresistive units, offset the adverse effect of the decrease in the magnetic field intensity of the magnetic scale sensed by the magnetoresistive units due to the increase in the distance on the hysteresis, and improve the repeat positioning accuracy of the entire linear position sensor. As Figure 6 shown, the abscissa represents the linear position after normalization processing, and the ordinate represents the repeat positioning accuracy. The linear position sensor proposed by the present invention has a repeat positioning accuracy of 1 - 2 μm, which has a significant improvement in repeat positioning accuracy compared with the linear position sensors existing in the market but not adopting the method proposed by the present invention.

[0011] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims involved.

Claims

1. A linear position sensor, characterized in that: The linear position sensor (10) includes a group of sensing elements, which are composed of a plurality of sensing elements arranged at a fixed pitch, and each sensing element is composed of a number of magnetoresistive units in the shape of curved lines; The linear position sensor (10) is used in cooperation with a magnetic scale (20), and the magnetic scale (20) is formed by alternately magnetizing poles with a specific pole length to form N poles and S poles, forming a periodic magnetic field distribution; the specific pole length is the fixed length of a single N pole or S pole; The fixed pitch of the sensing elements is set according to the pole length of the magnetic scale (20); The group of sensing elements of the linear position sensor (10) forms two Wheatstone bridges by combining a plurality of sensing elements; Each of the sensing elements includes I magnetoresistive units. For the i-th magnetoresistive unit, i = 1, 2, ..., I; the distance between the i-th magnetoresistive unit and the magnetic scale (20) is r i , when the distance increases, the width of the corresponding magnetoresistive unit also increases accordingly.

2. The linear position sensor according to claim 1, wherein: The magnetoresistive unit is formed by etching a magnetoresistive thin film into the shape of a curved line.

3. A linear position sensor according to claim 1, wherein: The magnetoresistive unit is selected from one of the three types: anisotropic magnetoresistance AMR, giant magnetoresistance GMR, and tunneling magnetoresistance TMR.

4. A linear position sensor according to claim 1, characterized in that: The specific pole length is set to p.

5. A linear position sensor according to claim 1, characterized in that: The fixed pitch of the sensing elements is set according to the pole length p and the type of the magnetoresistive unit: when the magnetoresistive unit is anisotropic magnetoresistance AMR, the fixed pitch is set to p / 4; when the magnetoresistive unit is giant magnetoresistance GMR and tunneling magnetoresistance TMR, the fixed pitch is set to p / 2.

6. A linear position sensor according to claim 1, characterized in that: The two Wheatstone bridges respectively sense the magnetic field angle distribution of the magnetic scale (20). When there is a relative linear motion between the sensing elements and the magnetic scale (20), the magnetoresistive units in the sensing elements sense the periodic magnetic field change on the surface of the magnetic scale (20), convert the magnetoresistance change in the magnetoresistive units into electrical signals through the two Wheatstone bridges, and respectively output two orthogonal sine signals Usin and cosine signals Ucos, and calculate the corresponding linear position according to these two signals.

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