Rotation angle detection method

Abstract

The invention discloses a rotation angle detection method, which comprises the following steps of: S1, selecting a plurality of point positions of a rotation angle of a detected object, collecting output voltages of Hall sensors of the point positions, and establishing a matched relational graph between the output voltages of the Hall sensors and the rotation angle of the detected object; and S2, collecting the output voltage y of the Hall sensor at the moment, if the output voltage y of the Hall sensor belongs to the matched point, reading the matched rotation angle of the measured object, and if the output voltage y of the Hall sensor at the moment belongs to the unmatched point, calculating the rotation angle x of the measured object at the moment. According to the principle of the technical scheme, the Hall sensor is arranged in a magnetic field, an included angle is formed between the axial direction of the Hall sensor and the magnetic field direction, at the moment, voltages at the two ends of the Hall sensor correspondingly change, and then the angle change between the axial direction of the Hall sensor and the magnetic field direction is compared and calculated according to the voltage change at the two ends of the Hall sensor. And convenience and rapidness are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of angle sensors, and in particular to a rotation angle detection method. Background Art

[0002] Existing angle detection devices, such as Chinese patent CN207703154U, disclose a Hall-type angle sensor acquisition and testing device, including: an execution device, a test device, an acquisition device and a conversion device; the execution device connects the test device and the acquisition device, the acquisition device outputs a signal to the back-end data processing mechanism, the test device connects the conversion device and the execution device, and the conversion device outputs a signal to the back-end data processing mechanism. Hall-type angle sensors are widely used in automotive electronics, such as electronic throttles, EPS electric power systems, etc. This type of sensor is mainly composed of a Hall chip and a magnet, and the angle value is fed back by changing the position of the magnet and outputting a voltage signal or a PWM signal duty cycle value.

[0003] The above technical solution has the following disadvantages: the calculation process is relatively complicated and inconvenient to use. Summary of the invention

[0004] The purpose of the present invention is to provide a rotation angle detection method for the above problems, which is convenient and quick to compare and calculate the angle change between the axial direction of the Hall sensor and the magnetic field direction according to the voltage change at both ends of the Hall sensor.

[0005] To achieve the above object, the present invention discloses a rotation angle detection method, comprising the following steps: Step S1, selecting several points of the rotation angle of the measured object, collecting the output voltages of the Hall sensors at these points, and establishing a matching relationship diagram between the output voltages of the Hall sensors and the rotation angles of the measured object.

[0006] Step S2, collecting the output voltage y of the Hall sensor at this time, if the output voltage y of the Hall sensor belongs to a matching point, then reading the matching rotation angle of the measured object, if the output voltage y of the Hall sensor at this time belongs to an unmatched point, then using the following formula to calculate the rotation angle x of the measured object at this time: ; Among them, y1 is the minimum matching voltage greater than the output voltage y of the Hall sensor at this time, y2 is the maximum matching voltage less than the output voltage y of the Hall sensor at this time, x1 is the minimum matching angle greater than the rotation angle x of the object under test at this time, and x2 is the maximum matching angle less than the rotation angle x of the object under test at this time.

[0007] The principle of this technical solution is to place the Hall sensor in a magnetic field so that the axial direction of the Hall sensor forms an angle with the direction of the magnetic field. At this time, the voltage at both ends of the Hall sensor changes accordingly. Then, based on the voltage change at both ends of the Hall sensor, the angle change between the axial direction of the Hall sensor and the direction of the magnetic field is compared and calculated, which is convenient and quick.

[0008] Preferably, in step S1, the number of points for selecting the rotation angle of the object to be measured is 15-20. Specifically, the number of points for selecting the rotation angle of the object to be measured can be 15, 17 or 20. It is convenient to use.

[0009] Preferably, in step S2, the MCU collects the output voltage y of the Hall sensor at this time, calculates the rotation angle x of the object under test at this time, and outputs a rotation angle signal of the object under test.

[0010] When the direction of the magnetic field changes, the MCU collects the output voltage of the Hall sensor, and then processes the signal through the MCU to calculate the corresponding angle. The MCU then outputs the voltage value at the corresponding point, which is convenient and fast.

[0011] Preferably, in step S2, the rotation angle signal voltage of the object under test output by the MCU is linearly related to the rotation angle x of the object under test at this time.

[0012] The output voltage of the MCU is linearly related to the rotation angle x of the object under test, which makes it convenient to directly read the rotation angle x of the object under test.

[0013] Preferably, the MCU is also connected to an anti-reverse connection circuit, an electrostatic protection circuit and a voltage amplification circuit.

[0014] When in use, the anti-reverse connection circuit and the electrostatic protection circuit are used to protect the MCU, the Hall sensor and the voltage amplifier circuit.

[0015] Preferably, the Hall sensor comprises an upper shell and a magnet seat which are independently arranged, a Hall chip is mounted on the upper shell, and two magnets which can adapt to the Hall chip are mounted on the magnet seat, and the two magnets are symmetrically arranged.

[0016] This structure uses a parallel configuration of the magnet and the Hall chip to provide a more balanced and stable magnetic field environment for the sensor. Specifically, the two magnets are arranged symmetrically and with opposite polarities, forming a closed magnetic circuit in the sensing area, so that the magnetic lines of force in this area have a smaller curvature and higher parallelism, thereby ensuring the sensor accuracy within a certain range.

[0017] This technical solution is suitable for applications in complex or demanding environments, such as agricultural machinery and other industrial fields. Since the mechanical friction common in traditional contact designs is eliminated, the fully separated angle sensor can provide a longer service life and higher operational safety. For application scenarios that require long-term stable operation, it is undoubtedly a more ideal option. This application uses the application of this technical solution in an electro-hydraulic lifting system as an example to illustrate, and does not limit the scope of application of this technical solution.

[0018] When in use, a bracket is installed on the frame, the upper shell is installed on the bracket, and the magnet seat is installed on the rotating shaft of the lifting arm. Using the Hall principle, the sensor itself and the magnet seat are physically isolated. This structural design not only effectively avoids the wear problem caused by direct contact, thereby reducing the accuracy loss and potential failure risks caused by wear; it also greatly simplifies the installation process and improves the fault tolerance of the system. The main advantages are significantly enhanced stability and reliability during the measurement process, reduced dependence on precise installation positions, reduced maintenance costs, and ultimately improved overall operating efficiency.

[0019] Preferably, a PCB is also installed on the upper shell, the Hall chip is electrically connected to the PCB, and the PCB is electrically connected with pins.

[0020] This structure is convenient for the installation of PCB and Hall chip and is easy to use.

[0021] Preferably, the upper shell is open on one side away from the magnet seat, an upper cover is installed on the open side of the upper shell, a plug is connected to the front side of the upper shell, the Hall chip and the PCB are located in the upper shell, and the end of the pin is located in the plug.

[0022] This structure is convenient for installing the pin and is easy to use.

[0023] Preferably, a magnet groove is provided on the side of the magnet seat, and the magnet is located in the magnet groove.

[0024] When installing the magnet, insert the magnet into the magnet slot, and an interference fit is adopted between the magnet and the side wall of the magnet slot, which is convenient for installation of the magnet and easy to use.

[0025] Preferably, a glue groove is provided on the inner side wall of the magnet groove.

[0026] When installing the magnet, the glue groove is used to pour epoxy resin glue, which fixes the magnet more firmly and prevents the magnet from detaching, making it easier to install the magnet and easier to use.

[0027] Preferably, a side of the upper shell body close to the magnet seat has a plurality of positioning claws, and the plurality of positioning claws are distributed circumferentially along the central axis of the upper shell body, and a corresponding ring-shaped positioning groove is opened on the side of the magnet seat close to the upper shell body.

[0028] When installing the upper shell and the magnet seat, the positioning claws are aligned with the positioning grooves to ensure the installation accuracy of the upper shell and the magnet seat and improve the detection accuracy.

[0029] Preferably, the magnet seat has a magnetic pole mark.

[0030] When installing the magnet, it is convenient to identify the installation direction of the magnet.

[0031] Preferably, an upper ear plate is connected to the upper shell body, an upper mounting hole is formed on the upper ear plate, a lower ear plate is connected to the magnet seat, a lower mounting hole is formed on the lower ear plate, an avoidance groove corresponding to the lower mounting hole is formed on the magnet seat, and a middle mounting hole is formed at the central axis of the magnet seat.

[0032] When installing the upper housing and the magnet seat, bolts are respectively used to pass through the upper mounting hole, the lower mounting hole and the middle mounting hole, which is easy to operate.

[0033] In summary, the beneficial effect of the present invention is that: the Hall sensor is placed in a magnetic field so that the axial direction of the Hall sensor forms an angle with the direction of the magnetic field. At this time, the voltage at both ends of the Hall sensor changes accordingly. Then, according to the voltage change at both ends of the Hall sensor, the angle change between the axial direction of the Hall sensor and the direction of the magnetic field is compared and calculated, which is convenient and quick. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of a rotation angle detection method of the present invention; Figure 2 It is a relationship diagram of the matching between the output voltage of the Hall sensor and the rotation angle of the object to be measured in a rotation angle detection method of the present invention; Figure 3 It is a schematic diagram of the front view stereoscopic structure of an angle sensor in a rotation angle detection method of the present invention; Figure 4 It is a rear-view stereoscopic structural schematic diagram of an angle sensor in a rotation angle detection method of the present invention; Figure 5 It is a schematic diagram of the internal structure of an angle sensor in a rotation angle detection method of the present invention; Figure 6 It is a schematic diagram of the three-dimensional structure of an upper shell in an angle sensor in a rotation angle detection method of the present invention; Figure 7 It is a schematic diagram of the three-dimensional structure of the lower shell of the angle sensor in a rotation angle detection method of the present invention; Figure 8 It is a three-dimensional structural schematic diagram of an angle sensor installation structure in a rotation angle detection method of the present invention; Fig. 9 yes Figure 8 Schematic diagram of the enlarged structure of part A in the figure.

[0035] In the figure: 1. upper shell; 2. upper cover; 3. upper ear plate; 4. upper mounting hole; 5. plug; 6. magnet seat; 7. magnet slot; 8. magnet; 9. lower ear plate; 10. lower mounting hole; 11. PCB; 12. Hall chip; 13. pin; 14. positioning claw; 15. positioning slot; 16. magnetic pole mark; 17. middle mounting hole; 18. avoidance slot; 19. frame; 20. lifting arm; 21. rotating shaft; 22. bracket; 23. protective cover; 24. glue slot; 25. upper insert; 26. lower insert. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0037] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0038] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0039] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0040] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments: like Figures 1 to 2 As shown, a rotation angle detection method comprises the following steps: Step S1, select several points of the rotation angle of the measured object, collect the output voltage of the Hall sensor at these points, and establish a relationship diagram of the matching between the output voltage of the Hall sensor and the rotation angle of the measured object. Specifically, in step S1, the number of points of the rotation angle of the measured object selected is 15-20. Specifically, the number of points of the rotation angle of the measured object selected can be 15, 17 or 20. Convenient to use.

[0041] Step S2, collecting the output voltage y of the Hall sensor at this time, if the output voltage y of the Hall sensor belongs to a matching point, then reading the matching rotation angle of the measured object, if the output voltage y of the Hall sensor at this time belongs to an unmatched point, then using the following formula to calculate the rotation angle x of the measured object at this time: ; Among them, y1 is the minimum matching voltage greater than the output voltage y of the Hall sensor at this time, y2 is the maximum matching voltage less than the output voltage y of the Hall sensor at this time, x1 is the minimum matching angle greater than the rotation angle x of the measured object at this time, and x2 is the maximum matching angle less than the rotation angle x of the measured object at this time. The principle of this technical solution is to place the Hall sensor in a magnetic field so that the axial direction of the Hall sensor and the direction of the magnetic field form an angle, at which time the voltage at both ends of the Hall sensor changes accordingly, and then compare and calculate the angle change between the axial direction of the Hall sensor and the direction of the magnetic field according to the voltage change at both ends of the Hall sensor, which is convenient and quick.

[0042] Specifically, in step S2, MCU collects the output voltage y of the Hall sensor at this time, calculates the rotation angle x of the measured object at this time, and outputs the measured object rotation angle signal. When the direction of the magnetic field changes, MCU collects the output voltage of the Hall sensor, and then performs signal processing through MCU to calculate the corresponding angle, and then MCU outputs the corresponding point voltage value, which is convenient and fast. Specifically, in step S2, the measured object rotation angle signal voltage output by MCU is linearly related to the rotation angle x of the measured object at this time. The output voltage through MCU is linearly related to the rotation angle x of the measured object at this time, which is convenient to directly read the rotation angle x of the measured object. MCU is also connected to an anti-reverse connection circuit, an electrostatic protection circuit and a voltage amplifier circuit. When in use, the anti-reverse connection circuit and the electrostatic protection circuit are used to protect MCU, Hall sensor and voltage amplifier circuit.

[0043] like Figures 3 to 7As shown, the Hall sensor includes an upper shell 1 and a magnet seat 6 which are independently arranged. A Hall chip 12 is installed on the upper shell 1, and a magnet 8 which can adapt to the Hall chip 12 is installed on the magnet seat 6. The upper shell 1 has a plurality of positioning claws 14 on one side close to the magnet seat 6, and the plurality of positioning claws 14 are distributed circumferentially along the central axis of the upper shell 1. The magnet seat 6 has a corresponding positioning groove 15 in the shape of a ring on one side close to the upper shell 1. Specifically, there are four positioning claws 14, and the four positioning claws 14 are evenly distributed circumferentially along the central axis of the upper shell 1. When installing the upper shell 1 and the magnet seat 6, the positioning claws 14 are aligned with the positioning groove 15 to ensure the installation accuracy of the upper shell 1 and the magnet seat 6 and improve the detection accuracy.

[0044] This technical solution is suitable for applications in complex or demanding environments, such as agricultural machinery and other industrial fields. Since the mechanical friction common in traditional contact designs is eliminated, the fully separated angle sensor can provide a longer service life and higher operational safety. For application scenarios that require long-term stable operation, it is undoubtedly a more ideal option. This application uses the application of this technical solution in an electro-hydraulic lifting system as an example to illustrate, and does not limit the scope of application of this technical solution.

[0045] When in use, a bracket 22 is installed on the frame 19, the upper shell 1 is installed on the bracket 22, and the magnet seat 6 is installed on the rotating shaft 21 of the lifting arm 20. Using the Hall principle, the sensor itself and the magnet seat are physically isolated. This structural design not only effectively avoids the wear problem caused by direct contact, thereby reducing the accuracy degradation and potential failure risks caused by wear; it also greatly simplifies the installation process and improves the fault tolerance of the system. The main advantages are reflected in significantly enhancing the stability and reliability of the measurement process, reducing the dependence on the precise installation position, reducing maintenance costs, and ultimately improving the overall operating efficiency.

[0046] The advantages of this technical solution are: the upper shell 1 and the magnet seat 6 are completely separated, that is, the two are measured without contact; the installation error tolerance is high, and a certain accuracy can be guaranteed within a certain axial and radial installation error range. The axial installation distance between the upper shell 1 and the magnet seat 6 has very little effect on the accuracy, and can be detected at a long distance, ensuring that the error is no more than 0.3° within 10mm.

[0047] Specifically, the upper housing 1 is also equipped with a PCB 11, the Hall chip 12 is electrically connected to the PCB 11, and the PCB 11 is electrically connected to the pin 13. This structure facilitates the installation of the PCB 11 and the Hall chip 12, and is easy to use. The upper housing 1 is open on one side away from the magnet seat 6, and the upper cover 2 is installed on the open side of the upper housing 1. The front side of the upper housing 1 is connected to the plug 5, the Hall chip 12 and the PCB 11 are located in the upper housing 1, and the end of the pin 13 is located in the plug 5. This structure facilitates the installation of the pin 13, and is easy to use.

[0048] Specifically, a magnet slot 7 is provided on the side of the magnet seat 6, and the magnet 8 is located in the magnet slot 7. When installing the magnet 8, the magnet 8 is inserted into the magnet slot 7, and an interference fit is adopted between the magnet 8 and the side wall of the magnet slot 7, which is convenient for the installation of the magnet 8 and easy to use. A glue slot 24 is provided on the inner side wall of the magnet slot 7. When installing the magnet 8, the glue slot 24 is used to pour epoxy resin glue, so that the magnet 8 is fixed more firmly, and the magnet 8 is prevented from detaching, which is convenient for the installation of the magnet 8 and easy to use. There are two magnet slots 7, and the two magnet slots 7 are arranged symmetrically with each other. This structure adopts a configuration mode in which the magnet and the Hall chip are parallel, which provides a more balanced and stable magnetic field environment for the sensor. Specifically, the two magnets 8 are arranged in a symmetrical and opposite polarity manner, forming a closed magnetic circuit in the sensing area, so that the magnetic lines of force in the area have a smaller curvature and a higher parallelism, thereby ensuring the sensor accuracy within a certain range. There is a magnetic pole mark 16 on the magnet seat 6. When installing the magnet 8, it is convenient to identify the installation direction of the magnet 8.

[0049] Specifically, the upper shell 1 is connected with an upper ear plate 3, and an upper mounting hole 4 is provided on the upper ear plate 3. The magnet seat 6 is connected with a lower ear plate 9, and a lower mounting hole 10 is provided on the lower ear plate 9. The magnet seat 6 is also provided with an avoidance groove 18 corresponding to the lower mounting hole 10, and a middle mounting hole 17 is provided at the central axis of the magnet seat 6. Specifically, an upper insert 25 is connected in the upper mounting hole 4, and a lower insert 26 is connected in the lower mounting hole 10. When installing the upper shell 1 and the magnet seat 6, bolts are used to pass through the upper mounting hole 4, the lower mounting hole 10 and the middle mounting hole 17, respectively, and the operation is simple.

[0050] like Figures 8 to 9 As shown, a mounting structure of the angle sensor as described in Example 1 includes a frame 19, a rotating shaft 21 is rotatably connected to the frame 19, a bracket 22 is mounted on the frame 19, an upper shell 1 is mounted on the bracket 22, and a magnet seat 6 is mounted on the rotating shaft 21. A shield 23 is also mounted on the frame 19. The shield 23 is used to protect the upper shell 1 and the magnet seat 6.

[0051] Using the Hall principle, the sensor itself is physically isolated from the magnet base. This structural design not only effectively avoids the wear problem caused by direct contact, thereby reducing the accuracy loss and potential failure risk caused by wear; it also greatly simplifies the installation process and improves the fault tolerance of the system. The main advantages are significantly enhanced stability and reliability during the measurement process, reduced dependence on precise installation positions, reduced maintenance costs, and ultimately improved overall operating efficiency.

[0052] Compared with the traditional angle sensor, which needs to be connected to the measured element, is prone to wear and tear in the use environment with low installation accuracy, or causes failures, and has complex installation and low fault tolerance, the fully separated angle sensor is completely separated from the measured object, and can still maintain reliable accuracy under certain axial and radial offsets and non-parallel installation conditions, which not only avoids wear and tear affecting accuracy or causing failures, but also improves installation convenience and installation fault tolerance. The fully separated angle sensor is designed for the electro-hydraulic lifting system of high-horsepower tractors, conforming to the trend of agricultural mechanization and automated operations, and has broad market prospects. The sensor detects angle changes with high precision, ensures the stability and reliability of the system, and improves agricultural production efficiency. At the same time, its superior performance is not only limited to tractor applications, but also suitable for engineering machinery such as excavators and loaders, to achieve accurate and reliable angle measurement, and improve operation accuracy and safety. In summary, the fully separated angle sensor has broad application prospects in the fields of agriculture and engineering machinery, and is of great significance to promoting the intelligent and automated development of related industries. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A rotation angle detection method, characterized in that: The following steps are involved: Step S1, selecting several points of the rotation angle of the measured object, collecting the output voltages of the Hall sensors at these points, and establishing a matching relationship diagram between the output voltages of the Hall sensors and the rotation angles of the measured object; Step S2, collecting the output voltage y of the Hall sensor at this time, if the output voltage y of the Hall sensor belongs to a matching point, then reading the matching rotation angle of the measured object, if the output voltage y of the Hall sensor at this time belongs to an unmatched point, then using the following formula to calculate the rotation angle x of the measured object at this time: ； Among them, y1 is the minimum matching voltage greater than the output voltage y of the Hall sensor at this time, y2 is the maximum matching voltage less than the output voltage y of the Hall sensor at this time, x1 is the minimum matching angle greater than the rotation angle x of the object under test at this time, and x2 is the maximum matching angle less than the rotation angle x of the object under test at this time.

2. The rotation angle detection method according to claim 1, characterized in that: In step S1, 15-20 points of rotation angles of the object to be measured are selected.

3. The rotation angle detection method according to claim 1, characterized in that: In step S2, the MCU collects the output voltage y of the Hall sensor at this time, calculates the rotation angle x of the object under test at this time, and outputs a rotation angle signal of the object under test.

4. The rotation angle detection method according to claim 3, characterized in that: In step S2, the rotation angle signal voltage of the measured object output by the MCU is linearly related to the rotation angle x of the measured object at this time.

5. The rotation angle detection method according to claim 3, characterized in that: The MCU is also connected to an anti-reverse connection circuit, an electrostatic protection circuit and a voltage amplifier circuit.

6. The rotation angle detection method according to any one of claims 1 to 5, characterized in that: The Hall sensor comprises an upper shell (1) and a magnet seat (6) which are independently arranged. A Hall chip (12) is mounted on the upper shell (1). Two magnets (8) which are compatible with the Hall chip (12) are mounted on the magnet seat (6). The two magnets (8) are symmetrically arranged.

7. The rotation angle detection method according to claim 6, characterized in that: A PCB (11) is also mounted on the upper housing (1), the Hall chip (12) is electrically connected to the PCB (11), and the PCB (11) is electrically connected to a plug pin (13); a side of the upper housing (1) away from the magnet seat (6) is open, an upper cover (2) is mounted on the open side of the upper housing (1), a plug (5) is connected to the front side of the upper housing (1), the Hall chip (12) and the PCB (11) are located in the upper housing (1), and an end of the plug pin (13) is located in the plug (5).

8. The rotation angle detection method according to claim 6, characterized in that: A magnet groove (7) is provided on the side of the magnet seat (6), and the magnet (8) is located in the magnet groove (7); a rubber groove (24) is provided on the inner wall of the magnet groove (7); and a magnetic pole mark (16) is provided on the magnet seat (6).

9. The rotation angle detection method according to claim 6, characterized in that: A side of the upper shell (1) close to the magnet seat (6) is provided with a plurality of positioning claws (14), the plurality of positioning claws (14) being distributed circumferentially along the central axis of the upper shell (1), and a side of the magnet seat (6) close to the upper shell (1) is correspondingly provided with a positioning groove (15) in the shape of an annulus.

10. The rotation angle detection method according to claim 6, characterized in that: An upper ear plate (3) is connected to the upper shell (1), an upper mounting hole (4) is formed on the upper ear plate (3), a lower ear plate (9) is connected to the magnet seat (6), a lower mounting hole (10) is formed on the lower ear plate (9), an avoidance groove (18) corresponding to the lower mounting hole (10) is formed on the magnet seat (6), and a middle mounting hole (17) is formed at the center axis of the magnet seat (6).

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