Wide-range absolute positioning electromagnetic induction type linear displacement sensor

Abstract

A wide-range absolute positioning electromagnetic induction type linear displacement sensor relates to the technical field of electromagnetic induction type displacement sensors, and comprises a transmit-receive board and an excitation board which can move relatively, and the transmit-receive board is provided with a transmitting winding and three three-phase receiving windings with different pitches; the excitation plate is provided with three rows of excitation coils which are equal to the three three-phase receiving windings in pitch and coincide with the three three-phase receiving windings in center line. The measuring circuit is provided with three parallel processing channels and is used for synchronously acquiring three corresponding phase quantization codes of a measured position in the fine pitch PF, the middle pitch PM and the coarse pitch PC after the transmitting winding is driven for one time; and directly calculating an absolute displacement value in the coarse pitch measuring range through an absolute positioning algorithm based on the three phase quantization codes. And the absolute displacement in the coarse pitch range is directly synthesized by calculating the integer pitch number step by step according to the integer wavelength ratio relationship of the coarse pitch, the medium pitch and the fine pitch. According to the invention, the breakthrough of the electromagnetic induction type displacement sensor from hybrid positioning to true absolute positioning is realized, and the sensor has the advantages of large measuring range, high precision, no data loss in power failure and low power consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic induction displacement sensor, and particularly relates to an electromagnetic induction linear displacement sensor for realizing absolute positioning in a large range by using multi-pitch phase solution. BACKGROUND

[0002] The electromagnetic induction displacement sensor is widely used in industrial measurement due to its advantages of strong anti-pollution ability and long service life. The prior art such as patent CN110487162A discloses a hybrid positioning electromagnetic induction displacement sensor, which measures the spatial phase in two different pitches, and uses the "mid displacement" for incremental accumulation to expand the range. Although this method realizes no range limitation, it is essentially incremental measurement, has a minimum measurement frequency requirement, and must be reset to zero after power failure to find the absolute position, and is not a real absolute positioning.

[0003] Another type of electromagnetic induction encoder as shown in patent CN112082580A only detects gap fluctuation or Y-axis offset through signal strength ratio, which is essentially a position abnormality alarm system and lacks real displacement measurement capability. The position relationship fluctuation between the detection head and the scale of the encoder only triggers an alarm signal (such as a gap overrun warning), and cannot output any absolute displacement value, which makes it completely unable to meet the high-precision positioning requirement. It relies on the design of multi-track width differentiation, and judges the position state through the signal strength ratio of tracks Tr1 / Tr2, which is strictly limited in application scenarios. Its detection accuracy is subject to mechanical gap stability, and when gap fluctuation or Y-axis displacement occurs, the signal strength significantly decays, resulting in a decrease in system reliability. Furthermore, it cannot realize position memory after power failure, and needs to be calibrated every time it is powered on, which violates the continuity requirement of industrial scenarios.

[0004] The prior art, such as patent CN101949682A discloses an absolute position measurement capacitive displacement sensor. Although the technology avoids analog conversion and arctangent operation by means of fluctuation driving signal and zero-crossing detection, it still has the following inherent limitations: first, its core is based on the principle of capacitive coupling, which requires high cleanliness and stability of the measurement environment. The humidity, oil pollution and parasitic capacitance changes of the medium between the sensor plates will directly interfere with the electric field, resulting in signal attenuation and measurement error, and the long-term reliability is insufficient in harsh industrial environments. Second, in order to realize pitch conversion and multi-wavelength measurement, the electrode system (transmission grid, reflection grid, conversion grid, receiving grid) structure is complex and the wiring is precise. Especially, the multiple conversion grid electrodes on the reflection plate need to be connected in order through wires and reflection grid, which requires high manufacturing process, increasing the production cost and failure rate. Third, the measurement process is essentially time-sharing and serial, which needs to switch the receiving signal path of different wavelengths through the switch group to complete the measurement of coarse, medium and fine wavelength displacement in turn, rather than truly parallel and synchronous, which limits the overall response speed of the system and the accuracy may be affected in high-speed motion state.

[0005] Therefore, there is an urgent need in the art for a new technical solution of displacement sensor that can fundamentally overcome the above-mentioned defects, has high reliability, high precision, large range, true absolute positioning ability and is easy to integrate. SUMMARY

[0006] In summary, the purpose of the present application is to realize a large-range absolute positioning electromagnetic induction type linear displacement sensor with high reliability, high precision, large range, true absolute positioning ability and easy integration.

[0007] In order to solve the technical problems proposed in the present application, the technical scheme adopted is: A large-range absolute positioning electromagnetic induction type linear displacement sensor, comprising a transceiver plate and an excitation plate that can move relative to each other, the transceiver plate is provided with a transmission winding and three three-phase receiving windings with different pitches; the three three-phase receiving windings are respectively a first three-phase receiving winding with a fine pitch P F , a second three-phase receiving winding with a medium pitch P M , and a third three-phase receiving winding with a coarse pitch P C , and P C >P M >P F ; the transmission winding surrounds the three three-phase receiving windings at the same time; the excitation plate is provided with three columns of excitation coils with the same pitch as the three three-phase receiving windings and the same center line; the sensor further comprises a measurement circuit with three parallel processing channels for synchronously acquiring the measured position at the fine pitch P F , the medium pitch P M and the coarse pitch P CThe corresponding first phase quantization code N F Second phase quantization encoding N M and the third phase quantization encoding N C Based on the first phase quantization encoding N F Second phase quantization encoding N M and the third phase quantization encoding N C The absolute displacement value within the coarse pitch range is directly calculated using an absolute positioning algorithm.

[0008] The beneficial effects of this invention are as follows: This invention achieves true absolute positioning, obtaining the absolute position across the entire coarse pitch range in a single measurement; data is not lost after power failure, and zeroing is not required. This is achieved by rationally setting the coarse pitch P. C It can achieve large-range measurements at the meter level and above. Inheriting the strong anti-interference capabilities of electromagnetic induction sensors, it employs parallel processing and hardware counting, resulting in fast measurement speed, no cumulative error, and high precision and reliability. The transceiver board and excitation board structure are compatible with existing hybrid positioning sensors. Through innovation in measurement algorithms and pitch design, it achieves a leap from "hybrid positioning" to "absolute positioning," facilitating industrialization, featuring a simple structure, ease of production, and simplified hardware design. It also possesses the low-power advantage of intermittent measurement mode. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the transceiver board and excitation board of the present invention; Figure 2 This is a block diagram illustrating the structural principle of the measurement circuit of the present invention; Figure 3 This is a flowchart of the method for obtaining absolute displacement values ​​according to the present invention; Figure 4 This is a schematic diagram of the transceiver board and excitation board according to another embodiment of the present invention. Detailed Implementation

[0010] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0011] Reference Figure 1 and Figure 2 As shown in the figure, the present invention discloses a large-range absolute positioning electromagnetic induction linear displacement sensor, comprising a transceiver board 1 and an excitation board 2 that are capable of relative movement. The transceiver board 1 is equipped with a transmitting winding 1.4 and three three-phase receiving windings with different pitches; the three-phase receiving windings are respectively finely pitched P F The first three-phase receiving winding 1.1, with a middle pitch P. M The second and third phase receiving windings 1.2 and coarse pitch P C The third three-phase receiving winding is 1.3, and P C >PM <P F， Also Figure 1 P1, P2 on the transceiver board 1 in P3 indicated by the distance corresponding to P C , P M And P F ; the transmitting winding 1.4 simultaneously surrounds three three-phase receiving windings; the excitation plate 2 is provided with three columns of excitation coils with equal pitch and coinciding center lines; the three columns of excitation coils are respectively the first column of excitation coils 2.1, the second column of excitation coils 2.2 and the third column of excitation coils 2.3; the sensor further comprises a measurement circuit with three parallel processing channels for synchronously acquiring the corresponding first phase quantization code N F , the second phase quantization code N M And the third phase quantization code N C After driving the transmitting winding 1.4 once, the measured position is in the fine pitch P F , the second phase quantization code N M And the third phase quantization code N C ; based on the first phase quantization code N F , the second phase quantization code N M And the third phase quantization code N C , the absolute displacement value in the coarse pitch range is directly calculated by the absolute positioning algorithm. Through the innovative "three-pitch parallel measurement and step-by-step absolute calculation" method, the absolute position in the entire range can be determined in one measurement without historical displacement data, realizing true absolute positioning.

[0012] In the specific implementation process, the preferred scheme is that the three columns of excitation coils of the excitation plate 2 are all short-circuit rings, and the size along the measurement path is half of the respective pitch. The transmitting winding 1.4 is a three approximately closed rectangular coil in the same direction in series, which respectively surrounds the first three-phase receiving winding 1.1 of the fine pitch P F , the second three-phase receiving winding 1.2 of the medium pitch P M And the third three-phase receiving winding 1.3 of the coarse pitch P C .

[0013] The core working principle of the application is: A driving pulse with extremely short duration is applied to the transmitting winding 1.4, and the linear time-varying magnetic field generated by the pulse simultaneously induces three-phase electromotive forces related to the relative position and not changing with time in the three three-phase receiving windings.

[0014] Three parallel signal processing channels synthesize the respective three-phase electromotive force into a discrete-time sinusoidal signal, and then through filtering, zero-crossing detection and addition counter counting, the first phase quantization encoding N F , the second phase quantization encoding N M and the third phase quantization encoding N C are obtained synchronously.

[0015] By using the wavelength constraint relationship among the coarse, medium and fine pitches, the integer pitch number representing the absolute position is directly solved through step-by-step solving, and finally the absolute displacement value of a large range is synthesized.

[0016] Preferably, the wavelength ratio of the three pitches is set to be co-prime, that is: The medium pitch P M =m*P F / (m-1); The medium range L M =P M *(m-1)=m*P F ; The coarse pitch P C =n*P M / (n-1)=m*n*P F / (m-1)*(n-1); The coarse range L C =P C *(n-1)=n*P M = m*n *P F / (m-1); Wherein, m and n are integers greater than 1.

[0017] Referring to Figure 3 shown, the absolute positioning algorithm comprises the following steps: a), calculate the pitch within quantization displacement difference of the coarse pitch P C and the medium pitch P M to obtain the coarse displacement X C : X C =[(N C -N M +2 P )mod2 P / 2 P ]*L C Wherein, the result of mod operation is taken in the range of [0,2 P -1]. 2 P is the system subdivision number; b), calculate the pitch within quantization displacement difference of the medium pitch P M and the fine pitch P FThe pitch quantization bit displacement difference is obtained M : X M =[(N M –N F +2 P )mod2 P / 2 P ]*L M Wherein, the result of the mod operation is taken in the range of [0,2 P -1] range. 2 P is the system subdivision number; c), gradually solve the integer pitch number: The pitch integer number K M =round[(X C -X M ) / P M ]; The detail pitch integer number K F =round[(X M -X F ) / P F ]; d), synthesis absolute displacement: X=K M *P M +K F *P F +X F .

[0018] The present application has the following features: 1、True absolute positioning: one measurement can obtain the absolute position in the entire coarse pitch range, the data is not lost after power failure, and there is no need to return to zero.

[0019] 2、Large range measurement: by reasonably setting the coarse pitch P C (For example, when P F =5.12mm, n=256, m=16, P M =5.46mm, P C =5.48mm, the total range can reach (16*5.12 / 15)*256=1398.1mm), which can realize the measurement of more than meter level.

[0020] 3、High precision and high reliability: it inherits the advantages of strong anti-interference ability of electromagnetic induction sensor, and adopts parallel processing and hardware counting, which has fast measurement speed and no cumulative error.

[0021] 4、Simple structure, easy to produce: the structure of the transceiver board and the excitation board is compatible with the existing hybrid positioning sensor, only through the innovation of measurement algorithm and pitch design, the leap from "hybrid positioning" to "absolute positioning" is realized, which is convenient for industrialization.

[0022] The present application realizes absolute positioning without historical data in an electromagnetic induction displacement sensor, has a large range of meters and high resolution of microns through integer wavelength ratio constraint and parallel calculation, adopts single transmission winding integrated with multiple pitch receiving windings in structure, simplifies hardware design, and can be disabled by a microcontroller, so that the sensor works in an intermittent measurement mode, has low power consumption and high reliability without data loss, and significantly improves industrial applicability. The present application significantly surpasses the prior art in technical principles, structural design, algorithm core and performance indicators.

[0023] Embodiment 1 The technical solutions of the present application are further described below with specific cases: The numerical values of the three-phase receiving windings with three different pitches are as follows: The pitch P of the fine-pitch three-phase receiving winding 1.1 F = 5.12 mm; The pitch P of the medium-pitch three-phase receiving winding 1.2 M = 5.46 mm; The pitch P of the coarse-pitch three-phase receiving winding 1.3 C = 5.48 mm.

[0024] The transmission winding 1.4 surrounds the above three three-phase receiving windings simultaneously to realize unified excitation of the magnetic field.

[0025] The pitch values of the three columns of excitation coils arranged on the excitation plate 2 are as follows: The pitch of the fine-pitch excitation coil 2.1 is equal to P F ; The pitch of the medium-pitch excitation coil 2.2 is equal to P M ; The pitch of the coarse-pitch excitation coil 2.3 is equal to P C .

[0026] The center lines of the excitation coils coincide with the center lines of the corresponding receiving windings, and the size along the measurement direction is half of the pitch.

[0027] As shown in Figure 2 , the measurement circuit includes: a driving module for applying a short-time pulse to the transmission winding; three parallel processing channels corresponding to the three three-phase receiving windings with different pitches; Each channel includes: a signal conditioning circuit for filtering and amplification, a zero-crossing detection circuit, and a phase quantization encoding N F , M , CThe acquired counter; when measuring, the driving module sends out pulses, three channels synchronously collect and process signals, and the phase encoding value N in three pitches is obtained F = 32, N M = 64, N C = 128, each encoding is 2 P integer value under subdivision, in the embodiment P = 12, that is, the subdivision number is 4096.

[0028] As Figure 3 shown, the solving process of the absolute displacement is as follows: Calculate the quantized displacement difference in the pitch: The coarse displacement amount: X C = [[(N C -N M + 2 P ) mod 2 P ] / 2 P ]*L C = ((128-64) / 4096)*(1397.4)=21.83mm; Wherein, the coarse range L C = P C *(n-1)=n*P M = m*n *P F / (m-1); L C = P C *(n-1), in the embodiment, n=256, so the coarse range L C = 5.48*255=1397.4mm.

[0029] The middle displacement amount: X M = [[(N M -N F + 2 P ) mod 2 P ] / 2 P ]*L M = (32 / 4096)*(81.9)=0.64 Wherein, the middle range L M = P M *(m-1), in the embodiment, m=16, so the middle range L M = 5.46*15=81.9mm.

[0030] The fine displacement amount: X F = (N X / 2 P )*P F= 32 / 4096 * 5.12 = 0.04mm Number of coarse pitch integers: K M = round[(X C -X M ) / P M ]= round[(X C -X M ) / P M ]= round[(21.83-0.64) / 5.46]= round(3.88)=4 Number of fine pitch integers: K F = round[(X M -X F ) / P F ]= round[(0.64-0.04) / 5.12]= round(0.12)=0 Wherein, round is a rounding function.

[0031] Synthetic absolute displacement: X=K M *P M +K F *P F +X F =4*5.46+0*5.12+0.04=21.84+0.04=21.88mm The final X is the absolute displacement value of the sensor within the coarse pitch range L C .

[0032] In this embodiment, the parameters are set as follows: P F =5.12mm,P M =5.14mm,P C =5.48mm m=16, n=256 System subdivision number 2 P =4096 P F / 2 P =5.12 / 4096≈0.00125mm, that is, the resolution can reach microns.

[0033] The measurement circuit can be controlled by a microcontroller to enter a disabled state, and the driving and processing circuits are turned off during the non-measurement period, and only when there is a displacement detection requirement, the system is awakened, so as to realize an intermittent measurement mode, significantly reduce the system power consumption, and be suitable for battery-powered or energy-saving scenes.

[0034] Embodiment 2 Referring to Figure 4 When the values of the three pitch-different three-phase receiving windings are respectively: The pitch P of the fine pitch three-phase receiving winding 1.1 F =4.78mm; The pitch P of the medium pitch three-phase receiving winding 1.2 M =5.10mm; The pitch P of the coarse pitch three-phase receiving winding 1.3 C =5.12mm.

[0035] The system subdivision number 2 P =4096 (i.e. P =12).

[0036] Suppose that after one measurement, the three phase quantization codes obtained synchronously are: N F =1000 N M =2000 N C =3000.

[0037] The pitch relationship is: P M =m*P F / (m-1) P C =n*P M / (n-1) m=16,n=256.

[0038] The range is: The medium range L M =P M *(m-1)=5.10mm×15=76.50mm The coarse range L C =P C *(n-1)=5.12mm×255=1305.60mm.

[0039] Calculate the three pitch-in quantization displacement differences (X C ,X M ,X F ): The coarse displacement X C X C =[(N C -N M +4096)mod 4096] / 4096×L C X C= [(3000 - 2000 + 4096) mod 4096] / 4096 x 1305.60 X C = [5096 mod 4096] / 4096 x 1305.60 X C =

[1000] / 4096 x 1305.60 X C ≈ 0.24414 x 1305.60 X C ≈ 318.75 mm.

[0040] Detail displacement X M X M = [(N M - N F + 4096) mod 4096] / 4096 x L M X M = [(2000 - 1000 + 4096) mod 4096] / 4096 x 76.50 X M = [5096 mod 4096] / 4096 x 76.50 X M =

[1000] / 4096 x 76.50 X M ≈ 0.24414 x 76.50 X M ≈ 18.68 mm.

[0041] Detail displacement X F X F = (NF / 4096) x P F X F = (1000 / 4096) x 4.78 X F ≈ 0.24414 x 4.78 X F ≈ 1.167 mm.

[0042] Step by step solve integer pitch number (K M , K F ): K M K M = round[ (X C - X M ) / P M ] K M = round[ (318.75 - 18.68) / 5.10 ] K M = round[ 300.07 / 5.10 ] K M = round[ 58.84 ] K M = 59。

[0043] Detail pitch integer number K F K F = round[ (X M - X F ) / P F ] K F = round[ (18.68 - 1.167) / 4.78 ] K F = round[ 17.513 / 4.78 ] K F = round[ 3.664 ] K F = 4。

[0044] Synthetic absolute displacement X X = K M * P M + K F * P F + X F X = (59 × 5.10) + (4 × 4.78) + 1.167 X = 300.90 + 19.12 + 1.167 X ≈ 321.187 mm。

[0045] This calculation result verifies that using only about 5mm pitch, through three pitch phase encoding and absolute positioning algorithm, the absolute position 321.187mm is successfully determined within a range of 1.3 meters in one measurement, perfectly embodying the characteristics of absolute positioning.

Claims

1. A large-range absolute positioning electromagnetic induction linear displacement sensor, comprising a transceiver board (1) and an excitation board (2) capable of relative movement, characterized in that: The transceiver board (1) is equipped with a transmitting winding (1.4) and three three-phase receiving windings with different pitches; the three-phase receiving windings are respectively fine pitch P F The first three-phase receiving winding (1.1), with a middle pitch P M The second and third phase receiving windings (1.2) and coarse pitch P C The third three-phase receiving winding (1.3), and P C >P M >P F The transmitting winding (1.4) simultaneously surrounds three three-phase receiving windings; The excitation plate (2) is provided with three rows of excitation coils, each with the same pitch as the three three-phase receiving windings and whose center lines coincide; the three rows of excitation coils are respectively the first row of excitation coils (2.1), the second row of excitation coils (2.2) and the third row of excitation coils (2.3). The sensor also includes a measurement circuit with three parallel processing channels for synchronously acquiring the measured position at the fine detail P after one drive of the transmitting winding (1.4). F Medium pitch P M and coarse pitch P C The corresponding first phase quantization code N F Second phase quantization encoding N M and the third phase quantization encoding N C Based on the first phase quantization encoding N F Second phase quantization encoding N M and the third phase quantization encoding N C The absolute displacement value within the coarse pitch range is directly calculated using an absolute positioning algorithm.

2. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 1, characterized in that: The three rows of excitation coils of the excitation plate (2) are all short-circuit rings, and their dimensions along the measurement path are half of their respective pitches.

3. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 1, characterized in that: The three pitches satisfy the following integer wavelength ratio relationship: Medium pitch P M =m*P F / (m-1); Medium range L M =P M *(m-1)=m*P F ; Coarse pitch P C =n*P M / (n-1)=m*n*P F / (m-1)*(n-1); Coarse range L C =P C *(n-1)=n*P M = m*n *P F / (m-1); Where m and n are integers greater than 1.

4. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 1, characterized in that: The absolute positioning algorithm includes the following steps: a) Calculate the coarse pitch P C With the middle pitch P M The coarse displacement X is obtained by quantizing the displacement difference within the pitch. C : X C =[(N C -N M +2 P )mod2 P / 2 P ]*L C The result of the modulo operation is in the range [0, 2]. P Within the range of -1].2 P The number of subdivisions in the system; b) Calculate the pitch P M With detail distance P F The displacement difference within the pitch is used to obtain the displacement X. M : X M =[(N M –N F +2 P )mod2 P / 2 P ]*L M The result of the modulo operation is in the range [0, 2]. P Within the range of -1]. 2 P The number of subdivisions in the system; c) Solving for integer pitch numbers step by step: Number of integer pitches K M =round[(X C -X M ) / P M ]; Number of integer distances to detail K F =round[(X M -X F ) / P F ]; Where round is the rounding function; d) Composite absolute displacement: X=K M *P M +K F *P F +X F .

5. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 1, characterized in that: The transmitting winding (1.4) consists of three approximately closed rectangular coils connected in the same direction, which respectively surround the first three-phase receiving winding (1.1) of fine pitch PF, the second three-phase receiving winding (1.2) of medium pitch PM and the third three-phase receiving winding (1.3) of coarse pitch PC.

6. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 1, characterized in that: The pitch P of the detailed pitch three-phase receiving winding (1.1) is described. F =5.12mm; The pitch P of the medium-pitch three-phase receiving winding (1.2) M =5.46mm; The pitch P of the coarse-pitch three-phase receiving winding (1.3) C =5.48mm.

7. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 6, characterized in that: Phase encoding value N within three pitches F =32,N M =64,N C =128, each code is 2 P ， in, P The integer value under the 12 subdivision is 4096.

8. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 7, characterized in that: The calculation process for absolute displacement is as follows: Calculate the quantized displacement difference within the pitch: Coarse displacement: X C =[[(N C -N M +2 P )mod2 P ] / 2 P ]*L C =((128-64) / 4096)*(1397.4)=21.83mm; Among them, coarse range L C =P C *(n-1)=n*P M = m*n *P F / (m-1); L C =P C *(n-1), n=256, coarse range L C =5.48×255=1397.4mm; Mid-displacement: X M =[[(N M -N F +2 P )mod2 P ] / 2 P ]*L M =(32 / 4096)*(81.9)=0.64; Among them, medium range L M =P M *(m-1), m=16, medium range L M =5.46×15=81.9mm; Fine displacement: X F =(N X / 2 P )*P F =32 / 4096*5.12=0.04mm; Number of integers in the middle pitch: K M =round[(X C -X M ) / P M ]= round[(X C -X M ) / P M ]=round[(21.83-0.64) / 5.46]= round(3.88)=4; Number of integer detail distances: K F =round[(X M -X F ) / P F ]= round[(0.64-0.04) / 5.12]= round(0.12)=0; Where, round is the rounding function; Composite absolute displacement: X=K M *P M +K F *P F +X F =4*5.46+0*5.12+0.04=21.84+0.04=21.88mm。 9. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 7, characterized in that: The measurement circuit is controlled by a microcontroller to enter a disabled state, shutting down the drive and processing circuits during non-measurement periods, and only waking up when there is a displacement detection requirement.

10. A large-range absolute positioning electromagnetic induction linear displacement sensor according to claim 1, characterized in that: The pitch P of the detailed pitch three-phase receiving winding (1.1) is described. F =4.78mm; The pitch P of the medium-pitch three-phase receiving winding (1.2) M =5.10mm; The pitch P of the coarse-pitch three-phase receiving winding (1.3) C =5.12mm.

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