Low-cost rotor displacement recognition method for eight-tooth pair-pole bearingless permanent-magnet sheet motor

Abstract

The application discloses a low-cost rotor displacement recognition method for an eight-tooth one-pair-pole bearingless permanent-magnet sheet motor, four programmable Hall sensors are sequentially installed on radial stator slots, and the Hall sensors are orthogonally distributed on the radial stator slots in pairs; the application proposes a four-phase Hall solving algorithm based on an extreme decoupling coefficient; firstly, an output signal expression of each Hall element is theoretically derived; secondly, other coefficients are separated through offline rotor edge sticking, and a variation extreme value of a single coefficient is obtained to measure and calculate a Hall signal coefficient, so that the constraint of the coefficient in the Hall signal is solved, and a demodulation process of multiplying a sine and a cosine to obtain the same coefficient proportional displacement information in the original method is cancelled; finally, rotor displacements x and y are solved through simultaneous equations and data summation and difference equations; the application is suitable for an eight-tooth one-pair-pole bearingless two-phase motor, and only four Hall sensors are needed to recognize the displacement, so that the cost is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of bearingless motor control technology, and mainly to a low-cost rotor displacement identification method for an eight-tooth, one-pole bearingless permanent magnet thin-film motor. Background Technology

[0002] Bearingless thin-plate motors, lacking a shaft and with separate stator and rotor, have a short axial length, making them easy to achieve five-degree-of-freedom levitation. This makes them uniquely applicable in ultra-clean medical fields such as cardiac pumps. Cardiac pumps require small size and stable levitation performance, but traditional bearingless control requires displacement sensors to sample displacement signals for closed-loop control. Commonly used displacement sensors, such as eddy current sensors, are large, expensive, and highly susceptible to environmental influences, failing to meet the requirements of small size and stable levitation performance in cardiac pumps. Therefore, a displacement-free algorithm is needed to replace displacement sensors.

[0003] Hall sensor-based displacement-free algorithms offer high signal-to-noise ratios, accurate displacement calculations, and excellent dynamic performance, making them a viable alternative to displacement sensors for closed-loop displacement detection. Existing displacement identification methods are all designed for bearingless three-phase six-tooth motors, where adjacent stator teeth are 60 degrees apart. Specifically, the patent "A Displacement-Free Method for the Rotor of a Bearingless Permanent Magnet Thin-Sheet Motor Based on Hall Sensors" (application number: 202111409320.9) uses 12 Hall sensors for displacement identification, while the patent "Rotor Displacement Identification Method for a Bearingless Permanent Magnet Thin-Sheet Motor in Start-up State" (application number: 202111623440.9) uses 6 Hall sensors and has a relatively complex algorithm. For bearingless two-phase motors, specifically eight-tooth single-pole motor structures with adjacent stator teeth 45 degrees apart, the 12 Hall sensor identification method, when used for a single-pole motor, only yields two projection equations in the same direction, resulting in linearly related equations that cannot be solved. Without considering magnetic leakage, the 6-Hall identification method obtains displacement information by multiplying three mutually exclusive Hall signals (120 degrees apart) by sine and cosine signals (120 degrees apart). However, for a single-pole 8-tooth motor, it's impossible to construct Hall signals with a 120-degree difference; only four mutually exclusive Hall signals (90 degrees apart) can be constructed. Following the above method, multiplying these by sine and cosine signals with a 90-degree difference and summing the results yields zero, containing no displacement information. Therefore, the method described in the patent cannot be directly applied to an 8-tooth single-pole motor. Furthermore, the existing technology uses too many Hall elements, resulting in a heavy cost burden. Summary of the Invention

[0004] Purpose of the invention: In view of the problems existing in the background technology, the present invention provides a low-cost rotor displacement identification method for an eight-tooth single-pole bearingless permanent magnet thin-film motor. On the one hand, it solves the problem that the existing technology cannot be well applied to the rotor displacement identification of an eight-tooth single-pole motor, and meets the application requirements of special bearingless two-phase motors. On the other hand, it uses four orthogonal Hall elements to identify displacement, which further reduces costs compared with the existing technology.

[0005] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0006] A low-cost rotor displacement identification method for an eight-tooth, one-pole, bearingless permanent magnet thin-film motor is disclosed. The bearingless permanent magnet thin-film motor adopts an eight-tooth, one-pole motor structure, including eight L-shaped stators. Each L-shaped stator includes an axial stator yoke and radial stator teeth, which surround the thin-film rotor. The radial stator teeth are flush with the rotor. Each axial stator yoke is wound with a suspension winding and a torque winding, respectively. The torque winding has one pair of poles, and the suspension winding has two pairs of poles, simultaneously realizing suspension control and rotation control. The bottom of the L-shaped stators is connected by an iron core magnetic ring. The thin-film rotor has no silicon steel sheets and a pair of permanent magnets are attached to its outer side. The magnetic field of the permanent magnets is sinusoidally distributed in space.

[0007] Four programmable Hall sensors, Hall1 to Hall4, are installed sequentially in the radial stator slots, with a 90-degree interval between adjacent Hall sensors. Based on the output signals of Hall1 to Hall4, the output signals of two opposite Hall sensors on the mechanical structure are summed to obtain two sum data. The sum data are then summed and subtracted. Based on experimentally measured coefficients of each Hall signal, the rotor radial displacements x and y are obtained.

[0008] Furthermore, the output signal of Hall1 is related to the rotor's displacement along and perpendicular to Hall1, the rotor angle, the permanent magnet flux linkage, and the axial disturbance. Since the thin-plate rotor does not have silicon steel sheets, the armature leakage flux is relatively large, so the leakage flux is ignored, and the output signal expression is as follows:

[0009] Hall1 = 0.5 * k1 * l * cos(θ) l -θ0)cos(ωt-θ0)+0.5*k2*l*sin(θ l -θ0)sin(ωt-θ0)+0.5*k4*cos(ωt-θ0)+δ

[0010] Where θ lωt represents the eccentric angle, l represents the eccentric length, ωt represents the rotor angle, and θ0 represents the mechanical angle where Hall1 is located. Taking the position of Hall1 as the reference, θ0 = 0 is taken; δ is the output change caused by axial vibration, k1 is the displacement coefficient along the Hall1 direction, k2 is the displacement coefficient perpendicular to the Hall1 direction, and k4 is the permanent magnet flux linkage coefficient when there is no eccentricity.

[0011] Since Hall1 and Hall3 are mechanically opposite each other, replacing θ0 with θ0+pi, the output signal of Hall3 is represented as follows:

[0012] Hall3=0.5*k1*l*cos(θ l -θ0)cos(ωt-θ0)+0.5*k2*l*sin(θ l -θ0)sin(ωt-θ0)-0.5*k4*cos(ωt-θ0)-δ

[0013] Similarly, the output signals of Hall2 and Hall4 can be obtained.

[0014] Furthermore, the output signals of the two opposing Hall sensors on the mechanical structure are summed to obtain two sum data: Hall1+Hall3 and Hall2+Hall4; specifically,

[0015] The output signals of Hall1 and Hall3 are added together to eliminate the effects of rotor axial vibration and permanent magnet flux linkage, as shown below:

[0016] Hall1 + Hall3 = k1 * l * cos(θ) l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)

[0017] Similarly, substituting θ0 + pi / 2 into θ0, we get Hall2 + Hall4 as follows:

[0018] Hall2 + Hall4 = k1 * l * sin(θ) l -θ0)sin(ωt-θ0)+k2*l*cos(θ l -θ0)cos(ωt-θ0)

[0019] Summing and subtracting the above data respectively, the results are as follows:

[0020] l1=Hall1+Hall3+Hall2+Hall4=(k1+k2)lcos(θ l -θ)

[0021] l2=Hall1+Hall3-Hall2-Hall4=(k1-k2)lcos(θ l +θ-2θ0).

[0022] Furthermore, the Hall signal coefficients k1 and k2 were obtained through experimental calculations; specifically,

[0023] When calculating k1, first fix the N pole of the motor rotor to the position directly opposite Hall1. First, attach the mechanically opposite Hall3 to the stator side, that is, attach the rotor corresponding to the mechanically opposite Hall3 to the stator side. Then attach Hall1 itself. Divide the increment of the output signal of Hall1 by the bilateral air gap to obtain k. 11 The double-sided air gap refers to the difference between the rotor's outer diameter and the stator's inner diameter; the above operations are performed sequentially on Hall2-Hall4 to obtain k respectively. 12 k 13 and k 14 Finally, the average value is calculated, which is the required Hall signal coefficient k1;

[0024] To calculate k2, first fix the motor rotor's N pole directly opposite Hall1. Manually move the rotor to the left, facing Hall3, and then to the right, facing Hall1, and finally to the stator side. Divide the Hall4 output signal increment (which is 90° clockwise from Hall1) by the bilateral air gap to obtain k. 21 The same principle applies to the operations on Hall2, Hall3, and Hall4; obtain k. 22 k 23 and k 24 Finally, calculate the average value, which is the required Hall signal coefficient k2.

[0025] Furthermore, by substituting the Hall signal coefficients k1 and k2 into the summation and subtraction results, the radial displacements x and y can be obtained as follows:

[0026]

[0027]

[0028] Beneficial effects:

[0029] (1) This invention proposes a four-phase Hall effect solution algorithm based on extreme value decoupling coefficients. The displacement-free method of patent 202111409320.9 is only applicable to motors with two or more pole pairs on the rotor. When applied to a single-pole motor, only one usable constraint can be obtained, and thus the displacement cannot be calculated. The displacement-free method of patent 202111623440.9 multiplies the spatial three-phase Hall signals by three-phase sine and cosine respectively, sums them, and processes them to obtain radial displacement information with the same proportion. When this method is used for an eight-tooth single-pole motor, the relative summation of the four Hall signals yields two effective signals. Analogous to a spatial two-phase Hall signal, the multiplied signals of the two-phase sine and cosine are opposites of each other. After multiplying the two-phase Hall signals by the opposite multiplied signals and summing them, only one constraint can be obtained, and the displacement cannot be calculated. If the relative summation is not considered, the method adopted in this invention can be regarded as a spatial four-phase Hall signal. The four-phase Hall signals are identical in pairs, and the multiplied signals of the four-phase sine and cosine are opposite in pairs, resulting in a summation of 0, which also does not contain a displacement signal. In summary, existing displacement identification methods are only applicable to motors with specific pole-slot combinations, and are not suitable for the eight-tooth single-pole motor scenario proposed in this invention. This invention proposes a four-phase Hall effect algorithm for eight-tooth single-pole motors. By offline rotor edge contact, other coefficients are separated, and the extreme values ​​of individual coefficient changes are obtained. This removes the constraints on the coefficients in the Hall signal and eliminates the demodulation process of multiplying by sine and cosine to obtain displacement information with the same coefficients, as in the original method. Summation and subtraction are then performed, and the displacement information is obtained by combining the results.

[0030] (2) This invention uses only 4 Hall sensors to identify displacement, further reducing costs. In the prior art, at least 6 Hall sensors are needed to remove the constraints of the coefficients, and the relative summation yields three sets of effective constraints to calculate two displacement information, which is redundant in an eight-tooth, one-pole motor. This invention uses 4 Hall sensors to obtain two sets of effective constraints, and removes the constraints on the coefficients by offline edge measurement, thus maximizing the use of Hall signals. Attached Figure Description

[0031] Figure 1 This is a framework diagram of the rotor displacement identification method provided by the present invention;

[0032] Figure 2 This is a schematic diagram of the mechanical position of the bearingless permanent magnet thin-film motor Hall sensor in this invention;

[0033] Figure 3 This is an axial cross-sectional view of the eight-tooth, one-pole, bearingless permanent magnet thin-film motor used in this invention;

[0034] Figure 4 This is a schematic diagram of the rotor eccentricity of the bearingless permanent magnet thin-film motor provided by the present invention;

[0035] Figure 5 This is an overall block diagram of a bearingless permanent magnet thin-film motor system using a displacement-free algorithm. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0037] The specific structure of the bearingless permanent magnet thin-film motor used in this embodiment is as follows: Figure 3 As shown, an eight-tooth, one-pole motor structure is adopted, including eight L-shaped stators 2. Each L-shaped stator 2 includes an axial stator yoke and radial stator teeth, which surround the thin-plate rotor. The radial stator teeth are flush with the rotor. Each axial stator yoke is wound with a suspension winding 4 and a torque winding 5. The torque winding has one pair of poles, and the suspension winding has two pairs of poles, realizing both suspension control and rotation control. The bottom of the L-shaped stators is connected by an iron core magnetic ring 3. A pair of permanent magnets is attached to the outside of the thin-plate rotor 1, and the magnetic field of the permanent magnets is sinusoidally distributed in space.

[0038] Here's a further explanation of what constitutes a pair of poles: A pair of poles refers to the number of sine waves of the magnetic field formed by the permanent magnet rotor in space. One NS distribution in space creates one sine wave because it has only one maximum and one minimum value. If it's an NSNS distribution, then it has two pairs of poles.

[0039] The following describes the specific implementation methods and beneficial effects of the present invention by adopting the displacement-free methods proposed in patents 202111409320.9 and 202111623440.9, as well as the displacement-free identification method provided by the present invention.

[0040] Both existing methods are for 6-tooth motors, i.e., for three Hall effect signals that are 120 degrees apart. For the 8-tooth, 1-pole motor scenario addressed in this invention, mechanical limitations prevent obtaining three Hall effect signals 120 degrees apart, but four Hall effect signals 90 degrees apart can be obtained using the methods described above. The expression is as follows:

[0041] Hall 1_eff =k1*l*cos(θ) l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)

[0042] Hall 2_eff =k1*l*cos(θ) l -θ0-pi / 2)cos(ωt-θ0-pi / 2)+k2*l*sin(θ l-θ0-pi / 2)sin(ωt-θ0-pi / 2)=k1*l*sin(θ l -θ0)sin(ωt-θ0)+k2*l*cos(θ l -θ0)cos(ωt-θ0)

[0043] Hall 3_eff =k1*l*cos(θ) l -θ0-pi)cos(ωt-θ0-pi)+k2*l*sin(θ l -θ0-pi)sin(ωt-θ0-pi)=k1*l*cos(θ l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)

[0044] Hall 4_eff =k1*l*cos(θ) l -θ0-3pi / 2)cos(ωt-θ0-3pi / 2)+k2*l*sin(θ l -θ0-3pi / 2)sin(ωt-θ0-3pi / 2)=k1*l*sin(θ l -θ0)sin(ωt-θ0)+k2*l*cos(θ l -θ0)cos(ωt-θ0)

[0045] First, according to the displacement-free method provided in patent 202111409320.9, the two sets of Hall signals that are 120 degrees apart are summed. Applied to the eight-tooth single-pole motor scenario of this invention, the above four Hall signals that are 90 degrees apart are summed. The summation result is as follows:

[0046] S = Hall 1_eff +Hall 2_eff +Hall 3_eff +Hall 4_eff = 2*(k1+k2)*l*cos(θ) l -ωt)

[0047] The summation result is the projection of the eccentric position at ωt, which is independent of the initial angle θ0. Therefore, when the above method is used in a one-pole motor scenario, it can only obtain two projection equations in the same direction, that is, linearly related equations, and cannot solve for the rotor displacement.

[0048] Then, regarding the displacement-free method provided in patent 202111623440.9, the displacement information is obtained by multiplying three Hall effect signals with a 120-degree difference in interval by sine and cosine signals with a 120-degree difference in interval. Applied to this embodiment, the displacement information is obtained by multiplying four Hall effect signals with a 90-degree difference in interval by sine and cosine signals with a 90-degree difference in interval as follows:

[0049] l1 = Hall 1_eff *cos(ωt-θ0)+Hall 2_eff *cos(ωt-θ0-pi / 2)+Hall 3_eff *cos(ωt-θ0-pi)+Hall 4_eff *cos(ωt-θ0-3pi / 2)=Hall 1_eff *cos(ωt-θ0)+Hall 2_eff *sin(ωt-θ0)-Hall 3_eff *cos(ωt-θ0)-Hall 4_eff *sin(ωt-θ0)=0

[0050] l2 = Hall 1_eff *sin(ωt-θ0)+Hall 2_eff *sin(ωt-θ0-pi / 2)+Hall 3_eff *sin(ωt-θ0-pi)+Hall 4_eff *sin(ωt-θ0-3pi / 2)=0

[0051] The result is 0, which does not contain displacement information and therefore cannot be calculated.

[0052] As the above conclusions show, for an eight-tooth, single-pole, bearingless permanent magnet thin-film motor, none of the existing displacement identification methods can obtain the rotor radial displacement. To address this specific scenario, this embodiment proposes a low-cost rotor displacement identification method with simpler calculation.

[0053] The displacement-free identification method used in this invention is as follows: Figure 1 As shown, four programmable Hall sensors, Hall1-Hall4, are sequentially installed in the radial stator slots, with a 90-degree interval between adjacent Hall sensors. Figure 2 As shown. Based on the output signals of Hall1-Hall4, the output signals of the two opposing Hall sensors on the mechanical structure are summed to obtain two sum data; the sum data are then summed and subtracted; based on experimentally measured coefficients of each Hall signal, the rotor radial displacements x and y are obtained. Specifically,

[0054] First, the output signals of Hall1 through Hall4 are derived. The output signal of Hall1 is related to the rotor displacement along and perpendicular to Hall1, the rotor angle, the permanent magnet flux linkage, and the axial disturbance. Since the thin-plate rotor does not have silicon steel sheets, the armature leakage flux is relatively large, so the leakage flux is ignored. The expression for the output signal is as follows:

[0055] Hall1 = 0.5 * k1 * l * cos(θ) l -θ0)cos(ωt-θ0)+0.5*k2*l*sin(θ l -θ0)sin(ωt-θ0)+0.5*k4*cos(ωt-θ0)+δ

[0056] like Figure 4 As shown, where θ l ωt represents the eccentric angle, l represents the eccentric length, ωt represents the rotor angle, and θ0 represents the mechanical angle where Hall1 is located. Taking the position of Hall1 as the reference, θ0 = 0 is taken; δ is the output change caused by axial vibration, k1 is the displacement coefficient along the Hall1 direction, k2 is the displacement coefficient perpendicular to the Hall1 direction, and k4 is the permanent magnet flux linkage coefficient when there is no eccentricity.

[0057] Since Hall1 and Hall3 are mechanically opposite each other, replacing θ0 with θ0+pi, the output signal of Hall3 is represented as follows:

[0058] Hall3=0.5*k1*l*cos(θ l -θ0)cos(ωt-θ0)+0.5*k2*l*sin(θ l -θ0)sin(ωt-θ0)-0.5*k4*cos(ωt-θ0)-δ

[0059] Similarly, the output signals of Hall2 and Hall4 can be obtained.

[0060] Then, the output signals of the two opposing Hall sensors on the mechanical structure are summed to eliminate the effects of rotor axial vibration and permanent magnet flux linkage, resulting in two sums, Hall1+Hall3 and Hall2+Hall4, as follows:

[0061] Hall1 + Hall3 = k1 * l * cos(θ) l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)

[0062] Similarly, substituting θ0 + pi / 2 into θ0, we get Hall2 + Hall4 as follows:

[0063] Hall2 + Hall4 = k1 * l * sin(θ) l -θ0)sin(ωt-θ0)+k2*l*cos(θ l -θ0)cos(ωt-θ0)

[0064] Summing and subtracting the above data respectively, the results are as follows:

[0065] l1=Hall1+Hall3+Hall2+Hall4=(k1+k2)lcos(θ l -θ)

[0066] l2=Hall1+Hall3-Hall2-Hall4=(k1-k2)lcos(θ l +θ-2θ0).

[0067] Next, the Hall signal coefficients k1 and k2 were obtained through experimental calculations; specifically,

[0068] When calculating k1, first fix the N pole of the motor rotor to the position directly opposite Hall1. First, attach the mechanically opposite Hall3 to the stator side, that is, attach the rotor corresponding to the mechanically opposite Hall3 to the stator side. Then attach Hall1 itself. Divide the increment of the output signal of Hall1 by the bilateral air gap to obtain k. 11 The double-sided air gap refers to the difference between the rotor's outer diameter and the stator's inner diameter; the above operations are performed sequentially on Hall2-Hall4 to obtain k respectively. 12 k 13 and k 14 Finally, the average value is calculated, which is the required Hall signal coefficient k1;

[0069] To calculate k2, first fix the motor rotor's N pole directly opposite Hall1. Manually move the rotor to the left, facing Hall3, and then to the right, facing Hall1, and finally to the stator side. Divide the Hall4 output signal increment (which is 90° clockwise from Hall1) by the bilateral air gap to obtain k. 21 With the N pole of the motor rotor facing Hall2, first attach it to Hall4 and then to Hall2. Divide the increment of the output signal from Hall1 by the bilateral air gap to obtain k. 22 Position the motor rotor's N pole directly opposite Hall 3, first attaching it to Hall 1 and then to Hall 3. Divide the increment of the Hall 2 output signal by the bilateral air gap to obtain k. 23 With the N pole of the motor rotor facing Hall 4, first attach it to the edge of Hall 2 and then to the edge of Hall 4. Divide the increment of the output signal from Hall 3 by the bilateral air gap to obtain k. 24 Finally, calculate the average value, which is the required Hall signal coefficient k2.

[0070] Substituting the Hall signal coefficients k1 and k2 into the summation and subtraction results, the radial displacements x and y can be obtained simultaneously as follows:

[0071]

[0072]

[0073] Figure 5 This is a block diagram of a bearingless permanent magnet thin-film motor system employing a displacement-free algorithm. The torque control section uses vector control, with an outer speed loop (using Hall effect sensors to calculate the speed as feedback) and an inner current loop. The displacement control section has an outer displacement loop (using Hall effect sensors to calculate the displacement using a displacement-free algorithm) and an inner current loop.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-cost rotor displacement identification method for an eight-tooth, one-pole, bearingless permanent magnet thin-film motor, wherein the bearingless permanent magnet thin-film motor adopts an eight-tooth, one-pole motor structure, including eight L-shaped stators; each L-shaped stator includes an axial stator yoke and radial stator teeth, surrounding a thin-film rotor, the radial stator teeth being flush with the rotor, each axial stator yoke having a suspension winding and a torque winding respectively, the torque winding having one pair of poles and the suspension winding having two pairs of poles, simultaneously achieving suspension control and rotation control; the bottom of the L-shaped stators is connected by an iron core magnetic ring; the thin-film rotor has no silicon steel sheets, and a pair of permanent magnets are attached to its outer side, the magnetic field of the permanent magnets being sinusoidally distributed in space; Its features are, Four programmable Hall sensors, Hall1 to Hall4, are sequentially installed in the radial stator slots, with a 90-degree interval between adjacent Hall sensors. Based on the output signals of Hall1 to Hall4, the output signals of two opposite Hall sensors on the mechanical structure are summed to obtain two sum data. The sum data is then summed again to obtain l1, and the difference data is then calculated to obtain l2. Based on experimentally measured coefficients of each Hall signal, the coefficients k1 and k2 of the Hall signals are substituted into the summation and difference results to obtain the radial displacements x and y as follows: Where θ0 represents the mechanical angle at which Hall1 is located.

2. The low-cost rotor displacement identification method for an eight-tooth, one-pole, bearingless permanent magnet thin-film motor according to claim 1, characterized in that, The output signal of Hall1 is related to the rotor's displacement along and perpendicular to Hall1, the rotor angle, the permanent magnet flux linkage, and the axial disturbance. Since the thin-plate rotor does not have silicon steel sheets, the armature leakage flux is relatively large, so the leakage flux is ignored. The output signal expression is as follows: Hall1=0.5*k1*l*cos(θ l -θ0)cos(ωt-θ0)+0.5*k2*l*sin(θ l -θ0)sin(ωt-θ0)+0.5*k4*cos(ωt-θ0)+δ Where θ l ωt represents the eccentric angle, l represents the eccentric length, and ωt represents the rotor angle. Taking the position of Hall1 as the reference, θ0 = 0 is taken. δ is the output change caused by axial jitter, k1 is the displacement coefficient along the Hall1 direction, k2 is the displacement coefficient perpendicular to the Hall1 direction, and k4 is the permanent magnet flux linkage coefficient when there is no eccentricity. Since Hall1 and Hall3 are mechanically opposite each other, replacing θ0 with θ0+pi, the output signal of Hall3 is represented as follows: Hall3=0.5*k1*l*cos(θ l -θ0)cos(ωt-θ0)+0.5*k2*l*sin(θ l -θ0)sin(ωt-θ0)-0.5*k4*cos(ωt-θ0)-δ Similarly, the output signals of Hall2 and Hall4 can be obtained.

3. The low-cost rotor displacement identification method for an eight-tooth, single-pole, bearingless permanent magnet thin-film motor according to claim 2, characterized in that, The output signals of two opposing Hall sensors on the mechanical structure are summed to obtain two sum data: Hall1+Hall3 and Hall2+Hall4; specifically, The output signals of Hall1 and Hall3 are added together to eliminate the effects of rotor axial vibration and permanent magnet flux linkage, as shown below: Hall1+Hall3=k1*l*cos(θ l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0) Similarly, substituting θ0 + pi / 2 into θ0, we get Hall2 + Hall4 as follows: Hall2+Hall4=k1*l*sin(θ l -θ0)sin(ωt-θ0)+k2*l*cos(θ l -θ0)cos(ωt-θ0) Summing and subtracting the above data respectively, the results are as follows: l1=Hall1+Hall3+Hall2+Hall4=(k1+k2)lcos(θ l -θ) l2=Hall1+Hall3-Hall2-Hall4=(k1-k2)lcos(θ l +θ-2θ0)。 4. The low-cost rotor displacement identification method for an eight-tooth, single-pole, bearingless permanent magnet thin-film motor according to claim 3, characterized in that, The Hall signal coefficients k1 and k2 were obtained through experimental calculations; specifically, When calculating k1, first fix the N pole of the motor rotor to the position directly opposite Hall1. First, attach the mechanically opposite Hall3 to the stator side, that is, attach the rotor corresponding to the mechanically opposite Hall3 to the stator side. Then attach Hall1 itself. Divide the increment of the output signal of Hall1 by the bilateral air gap to obtain k. 11 The double-sided air gap refers to the difference between the rotor's outer diameter and the stator's inner diameter; the above operations are performed sequentially on Hall2-Hall4 to obtain k respectively. 12 k 13 and k 14 Finally, the average value is calculated, which is the required Hall signal coefficient k1; To calculate k2, first fix the motor rotor's N pole directly opposite Hall1. Manually move the rotor to the left, facing Hall3, and then to the right, facing Hall1, and finally to the stator side. Divide the Hall4 output signal increment (which is 90° clockwise from Hall1) by the bilateral air gap to obtain k. 21 The same principle applies to the operations on Hall2, Hall3, and Hall4; obtain k. 22 k 23 and k 24 Finally, calculate the average value, which is the required Hall signal coefficient k2.

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