CN114689098B - Ultrasonic rotary encoder - Google Patents

Abstract

The invention relates to an ultrasonic rotary encoder which comprises a sensor part, a rotary transmission part and a signal processing part, wherein the sensor part comprises a stator, a rotor, an ultrasonic sensor and a plurality of grid bars, wherein the echo signals formed by the grid bars and the echo signals formed by the side walls of the stator are different in strength. According to the invention, more information can be obtained through the corresponding arrangement of the grids and the ultrasonic sensors, so that the ultrasonic rotary encoder can accurately calculate the rotation angle and the rotation speed of the stator, the error of the grids on ultrasonic echo detection is greatly reduced by combining the angular resolution precision of the encoder, and each movement period can be easily seen under the action of a single grid bar, so that the ultrasonic rotary encoder can conveniently and accurately judge.

Description

Ultrasonic rotary encoder

This application is a divisional application with a filing date of June 18, 2020, an application number of 2020105620646, and a grille forming process named ultrasonic rotary encoder.

Technical field

The invention belongs to the field of ultrasonic encoders, and specifically relates to an ultrasonic rotary encoder.

Background technique

Currently, rotary encoders are also called shaft encoders. They are mainly devices that convert rotational position or rotation amount into electronic signals. They can be used in industrial control, robotics, special lenses, etc.

Rotary encoders are mainly divided into two types: absolute encoders and incremental encoders. Incremental encoders use detection pulses to calculate the rotation speed and relative position and can output information about rotational motion; absolute encoders will output rotational speed. The absolute position of the axis can be regarded as an angle sensor.

Moreover, the operating modes of encoders are generally divided into mechanical, optical, electromagnetic, inductive and capacitive types. This type of sensor combines detection elements and processing circuits, and has a relatively large structure, generally with a diameter of more than 15mm. , it cannot be applied well in some fields with small structures.

At the same time, in the ultrasonic encoder, it mainly obtains the motion information of the rotating axis through the intensity of the ultrasonic echo. The intensity of the echo mainly depends on the grid, and the current grid generally consists of a large number of equal-spaced It is composed of parallel slits, usually an optical device, called a grating, which is divided into reflection grating, transmission grating, etc. The grid is generally a planar structure, usually formed by photolithography, laser cutting, etching and other technologies. It is to carve many parallel notches on the surface of a specific material such as glass or metal to form a transparent grating and a reflective grating. Staggered structure.

However, due to the high precision requirements and small size of gratings, it is very difficult to make gratings on cylindrical surfaces. Planar gratings are usually made by curling, which easily introduces errors at the curled joints.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a brand new ultrasonic rotary encoder.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

An ultrasonic rotary encoder, which includes a sensor part, a rotation transmission part, and a signal processing part. The sensor part includes a stator with a circular cross-section and a straight tube shape, and is arranged inside the stator to freely rotate around the centerline direction of the stator. The rotor, the ultrasonic sensor fixedly installed at the end of the rotor extending into the stator, and a plurality of grating bars evenly distributed around the circumference of the stator, in which the echo signal formed by the grating bars is consistent with the echo formed by the side walls of the stator. There is a difference in strength between signals, and a grid is formed between two adjacent grid bars. The grids set in sequence form a grid. There are multiple groups of grids, and each group of grids is distributed side by side along the length of the stator. , an angular deviation of 180°/N is formed between each adjacent two sets of grids. N is the number of grid bars. There are multiple ultrasonic sensors and they are correspondingly distributed in the ultrasonic echo detection area formed by the grids. One set of gratings and one ultrasonic sensor constitute a set of information acquisition units. Multiple sets of information acquisition units have information acquisition units with a single grating bar. Assuming that the lateral resolution is λ, the encoder has the highest angular resolution accuracy. is 360°/λ.

Preferably, an angular deviation of 180°/N is also formed between a single grating bar and an adjacent grating bar, where N is the number of grating bars. Under the action of a single grating bar, it is easy to see each movement cycle, which facilitates the ultrasonic rotary encoder to make accurate decisions.

Preferably, the echo signals formed by the grating strips are stronger than the echo signals formed by the stator side walls.

According to a specific implementation and preferred aspect of the present invention, the material of the stator is plastic or rubber, and the grating bars are formed of metal coating or are metal parts.

According to a specific implementation and preferred aspect of the present invention, a plurality of elongated slots are formed on the stator, each elongated slot is an arc segment with the center of the stator as the center, and each elongated slot extends along the length direction of the stator. Extend, wherein the grille bars correspond to the elongated groove one-to-one, and the grille bars are arranged in the elongated groove.

Preferably, the elongated slots are located on the outer wall of the stator, the slot depth of each elongated slot is equal, and the distance between the bottom surface of the slot and the corresponding inner wall of the stator is 1/6 to 1/2 of the stator wall thickness.

Preferably, the grating bars are metal coatings formed in the elongated grooves by spraying, evaporation or sputtering, and the thickness is equal to the groove depth of the corresponding elongated grooves.

Preferably, the rotor is the shaft to be detected, and its diameter is greater than or equal to 0.3mm; the inner diameter of the stator is greater than or equal to 0.4mm, and the outer diameter of the stator is greater than or equal to 0.5mm.

Preferably, a mounting groove extending along its length direction is formed at the end of the rotor, and a plurality of the ultrasonic sensors are arranged side by side in the mounting groove.

In addition, the above-mentioned grille forming process includes the following steps:

1) Evenly coat the inner wall or outer periphery of the stator and the surface corresponding to the position of the ultrasonic sensor with a layer of material that is easy to peel off from the surface of the stator;

2). Multiple elongated slots are formed on the wall of the stator by being recessed from the surface of the material layer. Each elongated slot has the same cross-section and is an arc segment with the center of the stator as the center. The elongated slots are evenly distributed around the circumference of the stator, and each elongated slot extends along the length direction of the stator;

3). Form a coating with a consistent thickness on the groove surface of the elongated groove and the surface of the material layer where the elongated groove is not formed. There is a gap between the echo signal formed by the coating and the echo signal formed by the stator side wall. Differences in strength and weakness;

4) Peel off the coated material layer from the surface of the stator. At the same time, the coating formed in each elongated groove is a grid bar, and a grid is formed between each two adjacent grid bars. , multiple grids arranged in sequence form the grid.

Preferably, the grid is located on the outer periphery of the stator. Before coating to form the material layer, the outer circumference of the stator is provided with a separation sleeve. The separation sleeve divides the stator into a grid area and a non-grid area. The material layer is coated on the grid. gate area, and in step 4), before or after peeling off the material layer, remove the separation sleeve from the periphery of the stator. The main purpose of setting up the separation sleeve is to: 1. Separate the grid area; 2. Prevent interference to the non-grid area during processing.

According to a specific implementation and preferred aspect of the present invention, the material layer in step 1) is a water-soluble glue layer, a water-insoluble glue layer or a film layer.

Preferably, the peeling means are arranged in one-to-one correspondence with the material layer. When the material layer is a water-soluble glue layer, the peeling means is dissolving; when the material layer is a water-insoluble glue layer, the peeling means is heating. Or light; when the material layer is a film layer (for example: parylene film), the peeling method is external force peeling.

According to another specific implementation and preferred aspect of the present invention, the material of the stator is plastic or rubber, and the grille bars are formed of metal coating or are metal parts. In this way, the echo signal formed by the grille bars is stronger than that of the stator side wall. The echo signal formed.

Preferably, the grid bars are arranged on the outer periphery of the stator. Before step 2), the inner support component is used to shape and support the inner wall of the stator. The long groove is cut by laser cutting or mechanical cutting, and after step 4) is completed, The inner support component is extracted from the inside of the stator. The setting of the inner support component is very simple, which is to prevent the deformation of the stator.

Furthermore, the groove depth of each elongated groove is equal, and the distance between the bottom surface of the groove and the corresponding inner wall of the stator is 1/6~1/2 of the stator wall thickness.

Preferably, in step 3), the coating is formed on the outer periphery of the stator by spraying, evaporation or sputtering. In this way, it is ensured that the thickness of each grating strip formed is equal, so the echo intensity provided by each grating strip is equal.

In addition, a mounting slot extending along the length of the rotor is formed at the end of the rotor. There are multiple ultrasonic sensors and they are arranged side by side in the mounting slot. There are multiple sets of grids that correspond to the ultrasonic sensors one-to-one. Each set of grids They are distributed side by side along the length direction of the stator, and an angular deviation of 180°/N is formed between each adjacent two sets of grids, where N is the number of grid bars. Through the corresponding settings of multiple grids and ultrasonic sensors, more information can be obtained, allowing the ultrasonic rotary encoder to accurately calculate the rotation angle and rotation speed of the stator.

Preferably, each grid and an ultrasonic sensor constitute a set of information acquisition units, and the ultrasonic rotary encoder further includes an information acquisition unit with a single grid bar, wherein the space between the single grid bar and the grids of adjacent grids There is also an angular deviation of 180°/N, where N is the number of grille bars. Under the action of a single grating bar, it is easy to see each movement cycle, which facilitates the ultrasonic rotary encoder to make accurate decisions.

Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

The present invention can obtain more information through the corresponding settings of multiple grids and ultrasonic sensors, so that the ultrasonic rotary encoder can accurately calculate the rotation angle and rotation speed of the stator, and greatly reduce the detection of ultrasonic echoes by the grid. Causes errors, and at the same time, under the action of a single grille bar, it is easy to see each movement cycle, which facilitates the ultrasonic rotary encoder to make accurate decisions.

Description of the drawings

Figure 1 is a schematic structural diagram (partial cross-section) of the ultrasonic rotary encoder of the present invention;

Figure 2a, Figure 2b, Figure 2c and Figure 2d are the corresponding state diagrams in step 1);

Figure 3a and Figure 3b are schematic diagrams of the corresponding states in step 2);

Figure 4a and Figure 4b are schematic diagrams of the corresponding states in step 3);

Figure 5a and Figure 5b are schematic diagrams of the corresponding states in step 4);

Figure 6 is a schematic structural diagram of the ultrasonic rotary encoder of the present invention (absolute encoder);

Among them: 1. Sensor part; 10. Stator; 11. Rotor; 110. Installation slot; 12. Ultrasonic sensor; 13. Grille bar; 2. Rotation transmission part; 20. Rotation part; 21. Information transmission part; 3. Signal processing part; 4. Inner support parts; 5. Separation sleeve; 6. Material layer; 7. Coating; s, grid area; f, non-grid area; c, elongated groove; q, information acquisition unit.

Implementation

In order to make the above objects, features and advantages of the present invention more obvious and easy to understand, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, the present invention can be implemented in many other ways different from those described here. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " "Back", "Left", "Right", "Vertical", "Horizontal", "Top", "Bottom", "Inside", "Outside", "Clockwise", "Counterclockwise", "Axis" The orientations or positional relationships indicated by "radial direction", "circumferential direction", etc. are based on the orientations or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply the device or device referred to. Elements must have a specific orientation, be constructed and operate in a specific orientation and therefore are not to be construed as limitations of the invention.

In addition, the terms “first” and “second” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Therefore, features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

In the present invention, unless otherwise clearly stated and limited, the terms "installation", "connection", "connection", "fixing" and other terms should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection. , or integrated into one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be an internal connection between two elements or an interactive relationship between two elements, unless otherwise specified restrictions. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

In the invention, unless otherwise expressly stated and limited, a first feature being "on" or "below" a second feature may be a direct contact between the first and second features, or an indirect contact between the first and second features through an intermediate medium. . Furthermore, the terms "above", "above" and "above" the first feature is above the second feature may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is higher in level than the second feature. "Below", "below" and "beneath" the first feature to the second feature may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature has a smaller horizontal height than the second feature.

It should be noted that when an element is referred to as being "mounted" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is said to be "connected" to another element, it can be directly connected to the other element or there may also be intervening elements present. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation manner.

As shown in Figure 1, the ultrasonic rotary encoder disclosed in this embodiment includes a sensor part 1, a rotary transmission part 2 (which can be a slip ring, a rotary transformer, a rotary capacitor, a rotary fiber coupler, etc.), and a signal processing part 3 , wherein the rotation transmission part 2 includes a rotation part 20 that drives the detected shaft to rotate around its own axis, and an information transmission part 21 connected with the sensor part 1 and the signal processing part 3. The detection information obtained by the sensor part 1 is transmitted by the information transmission part 21 To the signal processing part 3, the signal processing part 3 performs signal analysis to obtain measurement information.

The sensor part 1 includes a stator 10 with a circular cross-section and a straight tube shape, a rotor 11 freely rotatable around the center line of the stator 10 , and an ultrasonic sensor fixedly installed at the end of the rotor 11 extending into the stator 10 12. And a plurality of grating bars 13 evenly distributed around the circumference of the stator 10, where the echo signal formed by the grating bars 13 is stronger than the echo signal formed by the side walls of the stator, and two adjacent grating bars A grid is formed between 13, and the grids arranged in sequence form a grid. The ultrasonic sensor 13 is located in the ultrasonic echo detection area formed by the grid.

In this example, the stator 10 is a plastic part, and the grille bars 13 are metal parts.

Specifically, the rotor is the shaft to be detected, and its diameter is greater than or equal to 0.3mm; the inner diameter of the stator is greater than or equal to 0.4mm, and the outer diameter of the stator is greater than or equal to 0.5mm.

In this example, the outer diameter of the stator 10 is 1.0mm, the inner diameter of the stator is 0.8-0.9mm, and the outer diameter of the rotor 11 is 0.6mm.

Specifically, the grille forming process is as follows:

Referring to Figures 2a to 2d (Figure 2a is the main view, Figure 2b is the right view; Figure 2c is the main view, and Figure 2d is the right view), 1), use the inner support component 4 to be shaped and supported on the inner wall of the stator 10, and then A separation sleeve 5 is placed on the outer circumference of the stator 10 to divide the stator 10 into a grid area s and a non-grid area f. Then, the outer circumference of the stator 10 in the grid area s is coated with a material layer that is easy to peel off from the surface of the stator. 6;

2). Multiple elongated grooves c are processed inwardly from the surface of the material layer 6 and formed on the wall of the stator 10 (shown in conjunction with Figure 3a, which is the main view), in which the cross-section of each elongated groove c is the same. , are arc segments with the center of the stator as the center of the circle (shown in Figure 3b, which is a right view from the middle of the elongated slot), multiple elongated slots are evenly distributed around the circumference of the stator, and each long slot The shaped groove extends along the fixed length direction;

3), form a coating 7 with a consistent thickness on the groove surface of the elongated groove c and the surface of the material layer 6 without the elongated groove (see Figure 4a and Figure 4b, where Figure 4a is the main view, Figure 4b is the elongated Right view of the middle of the slot), where the echo signal formed by coating 7 is stronger than the echo signal formed by the side wall of stator 10;

4) Peel off the material layer 6 with the coating 7 formed on the surface of the stator 10 (as shown in Figure 5a and Figure 5b, where Figure 5a is the main view and Figure 5b is the right view from the middle of the elongated groove) , and pull out the inner support member 4 from the inside of the stator 10. At this time, the coating formed in each elongated groove c is a grid bar 13, and a grid is formed between each two adjacent grid bars 13. , multiple grids arranged in sequence form the grid.

In order to further facilitate the above-mentioned grille forming, the following methods are also used in this example.

In step 1), the material layer is a glue layer that is soluble in water. In this way, once the grille is formed, the entire stator is placed in water, and the material layer on the surface of the stator is quickly removed due to the dissolution of the material layer.

Of course, you can also use a water-insoluble glue layer and corresponding means of heating (or light to degumming it), parylene film layer and external force peeling to facilitate the peeling of the material layer.

In step 2), the so-called processing refers to mechanical processing or laser processing, but it is worth reminding that the groove depth of each long groove is equal, and the distance between the bottom surface of the groove and the corresponding inner wall of the stator is the thickness of the stator wall. 3/5.

Preferably, in step 3), the coating is formed on the outer periphery of the stator by spraying, evaporation or sputtering while keeping the stator rotating. In this way, it is ensured that the thickness of each grating strip formed is equal, so the echo intensity provided by each grating strip is equal.

In this example, the metal material is a sound-reflecting material, such as stainless steel, gold, aluminum, and other materials, and is formed in a long slot on the outer periphery of the stator through evaporation.

As shown in FIG. 6 , a mounting groove 110 extending along the length direction of the rotor 11 is formed at the end of the rotor 11 . There are multiple ultrasonic sensors 12 arranged side by side in the mounting groove 110 . The grid corresponds to the ultrasonic sensors 12 one by one, and The formed ultrasonic echo detection areas are distributed side by side along the length direction of the stator 10, and an angular deviation of 180°/N is formed between each adjacent two sets of grids, where N is the number of grid bars. Through the corresponding settings of multiple grids and ultrasonic sensors, more information can be obtained, allowing the ultrasonic rotary encoder to accurately calculate the rotation angle and rotation speed of the stator.

Each grid and an ultrasonic sensor 13 form a set of information acquisition units q. The ultrasonic rotary encoder also includes an information acquisition unit q with a single grid bar, where the single grid bar 13 is connected to the grid of the adjacent grid. There is also an angular deviation of 180°/N, where N is the number of grille bars. Under the action of a single grating bar, it is easy to see each movement cycle, which facilitates the ultrasonic rotary encoder to make accurate decisions.

Therefore, in this example, there are three groups of information acquisition units q, which are 3-bit Gray codes, which are absolute encoders.

Similarly, the number of Gray code bits can be increased by increasing the number of scale rows and ultrasonic sensors, thereby improving the encoder resolution.

In addition, taking an ultrasonic probe with a center frequency of 50MHz as an example, its lateral resolution is about 200um. The size of this resolution determines that the minimum scale spacing of the grating bars on the stator cannot be less than the lateral resolution of the ultrasonic probe, so that it can obtain Strong and weak signals required.

Assuming that the lateral resolution is λ, the angular resolution accuracy of the encoder is up to 360°/λ. But we can improve the accuracy of the encoder by increasing the number of sensors.

To sum up, in this embodiment, the sensor is designed using the strength of the echoes reflected by different reflectors when the ultrasonic wave encounters it, and the principle of rotational encoding is used to measure the rotation speed and position of the rotating object.

At the same time, using ultra-high frequency micro-ultrasonic sensors, the encoder structure can be designed to measure the rotation speed and position of the detected shaft with a diameter of more than 0.3mm. Therefore, it can be used in high-precision detection fields, such as In vivo interventional medical imaging equipment can effectively correct image distortion (NURD) caused by rotational distortion to ensure image accuracy, which has very good advantages.

The detection process of this embodiment is as follows:

(1) The rotor is replaced by the detected shaft, and a mounting slot is formed at the end of the rotor. The ultrasonic sensors are distributed in the mounting slot and located in the ultrasonic echo detection area formed by multiple grid bars;

(2) Start the rotating transmission part and the ultrasonic sensor, and collect the ultrasonic echo signal under the synchronous rotation of the detected shaft and the ultrasonic sensor. When the emission surface of the ultrasonic sensor is parallel to the tangent of each grid bar, the echo is reflected The intensity is maximum Amax. When the emission surface of the ultrasonic sensor is facing the middle position of two adjacent grating strips, the reflected echo intensity is the weakest Amin. When the emission surface of the ultrasonic sensor is at other positions, the reflected echo intensity is between Amax and between Amin;

(3) The ultrasonic sensor transmits the collected reflected echo intensity to the signal processing part, which performs data analysis and imaging. The rotation speed and rotation angle of the detected shaft can be calculated based on the imaging information.

At the same time, in order to further improve the resolution of the encoder, in the above step (1), three groups of information acquisition units can be set side by side to form a three-bit Gray code. Of course, multiple groups of side-by-side multi-bit Gray codes can also be used. Detection is carried out, so that the motion data of the detected axis can be obtained more accurately.

The above detailed description of the present invention is intended to enable those familiar with the art to understand the content of the present invention and implement it. This does not limit the scope of protection of the present invention. Any work made based on the spirit of the present invention, etc. Effective changes or modifications shall be included in the protection scope of the present invention.

Claims (10)

1. An ultrasonic rotary encoder, characterized in that: the ultrasonic rotary encoder includes a sensor part, a rotation transmission part, and a signal processing part. The sensor part includes a stator with a circular cross-section and a straight tube shape. The rotor is freely rotatable in the direction of the center line of the stator, the ultrasonic sensor is fixedly provided at the end of the rotor extending into the stator, and a plurality of grid bars evenly distributed around the circumference of the stator, wherein the grid bars form There is a strength difference between the echo signal and the echo signal formed by the stator side wall, and a grid is formed between each two adjacent grid bars, and the grids arranged in sequence form a grid, so There are multiple groups of the grids, each group of the grids is distributed side by side along the length direction of the stator, and an angular deviation of 180°/N is formed between each adjacent two groups of grids, where N is the number, there are multiple ultrasonic sensors and they are distributed correspondingly in the ultrasonic echo detection area formed by the grating, wherein one set of gratings and one ultrasonic sensor constitute a set of information acquisition units, and multiple sets of all The information acquisition unit has a single information acquisition unit of the grating bar, and assuming that the lateral resolution is λ, the angular resolution accuracy of the encoder is up to 360°/λ. 2. The ultrasonic rotary encoder according to claim 1, characterized in that: an angular deviation of 180°/N is also formed between a single grating bar and the adjacent gratings, and N is The number of grill bars. 3. The ultrasonic rotary encoder according to claim 1, wherein the echo signal formed by the grating strips is stronger than the echo signal formed by the stator side wall. 4. The ultrasonic rotary encoder according to claim 3, wherein the stator is made of plastic or rubber, and the grating bars are formed of metal coating or are metal parts. 5. The ultrasonic rotary encoder according to claim 1, characterized in that: a plurality of elongated slots are formed on the stator, and each of the elongated slots is an arc segment with the center of the stator as the center of the circle. , and each elongated slot extends along the length direction of the stator, wherein the grid bars correspond to the elongated slots one-to-one, and the grid bars are arranged in the elongated slots. 6. The ultrasonic rotary encoder according to claim 5, characterized in that: the elongated slots are located on the outer wall of the stator, the slot depth of each of the elongated slots is equal, and the bottom surface of the slot is equal to the corresponding position. The distance between the inner walls of the stator is 1/6~1/2 of the stator wall thickness. 7. The ultrasonic rotary encoder according to claim 6, wherein the grating strips are metal coatings formed in the elongated grooves by spraying, evaporation or sputtering, and have a thickness corresponding to The groove depths of the elongated grooves are equal. 8. The ultrasonic rotary encoder according to claim 1, characterized in that: the rotor is a detected shaft, and the diameter is greater than or equal to 0.3mm; the inner diameter of the stator is greater than or equal to 0.4mm, and the outer diameter of the stator is greater than or equal to 0.4mm. Greater than or equal to 0.5mm. 9. The ultrasonic rotary encoder according to claim 1, wherein a mounting groove extending along its length direction is formed at the end of the rotor, and a plurality of the ultrasonic sensors are arranged side by side in the mounting groove. . 10. The ultrasonic rotary encoder according to claim 1, characterized in that: the grid forming process includes the following steps: 1). Evenly coat the inner wall or outer periphery of the stator and the surface corresponding to the position of the ultrasonic sensor with a material layer that is easy to peel off from the surface of the stator. The material layer is a water-soluble glue layer. Water-insoluble glue layer or film layer; 2). Multiple elongated slots are formed on the wall of the stator by being recessed from the surface of the material layer. Each elongated slot has the same cross-section and is an arc segment with the center of the stator as the center. The elongated slots are evenly distributed around the circumference of the stator, and each elongated slot extends in the length direction along the stator; 3). Form a coating with a consistent thickness on the groove surface of the elongated groove and the surface of the material layer without the elongated groove, wherein the echo signal formed by the coating is equal to the echo signal formed by the stator side wall. There are differences in strength and weakness between; 4) Peel off the material layer with the coating on the surface from the surface of the stator. The peeling method is dissolution or heating or light or external force peeling. At the same time, the coating formed in each elongated groove is a grid bar. A grid is formed between every two adjacent grid bars, and multiple grids arranged in sequence form the grid.