CN114689098B

CN114689098B - Ultrasonic rotary encoder

Info

Publication number: CN114689098B
Application number: CN202210276009.XA
Authority: CN
Inventors: 韩志乐; 简小华
Original assignee: Suzhou Institute of Biomedical Engineering and Technology of CAS
Current assignee: Suzhou Institute of Biomedical Engineering and Technology of CAS
Priority date: 2020-06-18
Filing date: 2020-06-18
Publication date: 2024-01-16
Anticipated expiration: 2040-06-18
Also published as: CN114689098A; CN111748770B; CN114689097B; CN114689097A; CN111748770A

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

The application is a divisional application of a grid forming process of which the application date is 18/6/2020, the application number is 2020105620646 and the name is an ultrasonic rotary encoder.

Technical Field

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

Background

At present, rotary encoders, also called shaft encoders, are mainly devices for converting a rotational position or a rotational amount into an electronic signal, and are applicable to industrial control, robotics, dedicated lenses, and the like.

The rotary encoders are mainly divided into an absolute encoder and an incremental encoder, the incremental encoder calculates the rotating speed and the relative position by using a detection pulse mode and can output information related to rotary motion; the absolute encoder outputs the absolute position of the rotation shaft and can be regarded as an angle sensor.

In addition, the operation modes of the encoder are generally classified into mechanical type, optical type, electromagnetic type, induction type, capacitance type and the like, the sensor combines a detection element and a processing circuit, the structure is relatively large, the diameter is generally more than 15mm, and the encoder cannot be well applied to some fields with narrow structures.

Meanwhile, in an ultrasonic encoder, the motion information of a rotation axis is mainly obtained by the echo intensity of ultrasonic, so that the intensity of the echo is mainly determined by a grating, and the current grating is generally formed by a large number of parallel slits with equal width and interval, and is generally called an optical device, and is divided into a reflection grating, a transmission grating and the like. The grid is generally a planar structure, and is usually formed by photolithography, laser cutting, etching and other techniques, and is a staggered structure in which a plurality of parallel scores are engraved on the surface of a specific material such as glass or metal to form a light-transmitting grid and a light-reflecting grid.

However, because the grating has high requirements on precision and small size, the difficulty in manufacturing the grating on the cylindrical surface is high, and the grating is generally manufactured by a method of curling a planar grating, so that errors are easily introduced at the curled joint.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects of the prior art and providing a brand-new ultrasonic rotary encoder.

In order to solve the technical problems, the invention adopts the following technical scheme:

the ultrasonic rotary encoder comprises a sensor part, a rotary transmission part and a signal processing part, wherein the sensor part comprises a stator with a circular cross section and a straight pipe shape, a rotor which is freely rotatably arranged in the stator around the central line direction of the stator, an ultrasonic sensor which is fixedly arranged at the end part of the rotor extending into the stator, and a plurality of grid bars which are uniformly distributed around the circumference of the stator, wherein the echo signals formed by the grid bars and the echo signals formed by the side wall of the stator are different in strength, grids are formed between every two adjacent grid bars, the grids sequentially arranged form a grid, the grids are provided with a plurality of groups, each group of grids are distributed side by side along the length direction of the stator, the angle deviation of 180 degrees/N is sequentially formed between every two adjacent groups of grids, N is the number of the grid bars, the ultrasonic sensor is a plurality of ultrasonic sensor and is correspondingly distributed in an ultrasonic echo detection area formed by the grids, one group of grids and one ultrasonic sensor form one group of information acquisition units, the information acquisition unit is provided with a single grid bar, and the angle of the encoder is 360 degrees/lambda of maximum accuracy.

Preferably, an angular deviation of 180 °/N is also formed between the individual grating bars and the adjacent grating bars, N being the number of grating bars. Under the action of a single grating strip, each movement period can be easily seen, so that the ultrasonic rotary encoder can conveniently and accurately judge.

Preferably, the grid strips form echo signals that are stronger than those formed by the stator side walls.

According to a specific and preferred aspect of the present invention, the stator is made of plastic or rubber, and the grid strips are formed by a metal coating or are metal pieces.

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 has an arc section centered on a center of the stator, and each elongated slot extends in a length direction along the stator, wherein the grid bars are in one-to-one correspondence with the elongated slots, and the grid bars are disposed in the elongated slots.

Preferably, the long grooves are positioned on the outer wall surface of the stator, the groove depth of each long groove is equal, and the distance between the groove bottom surface and the inner wall of the stator at the corresponding position is 1/6-1/2 of the wall thickness of the stator.

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

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

Preferably, the rotor end portion is formed with a mounting groove extending in a longitudinal direction thereof, and the plurality of ultrasonic sensors are arranged in parallel in the mounting groove.

In addition, the grid forming process comprises the following steps:

1) Uniformly coating a material layer which is easy to peel off from the surface of the stator on the surface of the inner wall or the periphery of the stator and corresponding to the position of the ultrasonic sensor;

2) A plurality of long grooves which are concavely processed inwards from the surface of the material layer and are formed on the wall surface of the stator, wherein the section of each long groove is the same, each long groove takes the center of the stator as an arc section of the circle center, the plurality of long grooves are uniformly distributed around the circumference of the stator, and each long groove extends along the length direction;

3) Forming a coating with consistent thickness on the groove surface of the long groove and the surface of the material layer, wherein the echo signals formed by the coating and the echo signals formed by the side wall of the stator have strength difference;

4) And stripping the material layer with the coating on the surface from the surface of the stator, wherein the coating formed in each long groove is a grid strip, one grid is formed between every two adjacent grid strips, and a plurality of grids which are sequentially arranged form the grid.

Preferably, the grid is located at the outer periphery of the stator and the stator is provided with a spacer sleeve around the periphery thereof before the coating to form the material layer, wherein the spacer sleeve divides the stator into a grid zone and a non-grid zone, the material layer is coated on said grid zone, and in step 4) the spacer sleeve is removed from the periphery of the stator before or after the material layer is peeled off. The arrangement of the separation sleeve has the main purposes that: 1. realizing the separation of the grid areas; 2. preventing interference to non-grating area during processing.

According to a specific 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 stripping means are arranged in one-to-one correspondence with the material layers, and when the material layers are water-soluble glue layers, the stripping means are dissolved; when the material layer is a water-insoluble adhesive layer, the stripping means is heating or illumination; when the material layer is a film layer (such as parylene film), the peeling means is external force peeling.

According to a further embodiment and preferred aspect of the invention, the stator is made of plastic or rubber and the grating strips are formed of a metal coating or of a metal piece, so that the echo signals formed by the grating strips are stronger than those formed by the side walls of the stator.

Preferably, the grid strips are arranged on the periphery of the stator, the inner support member is used for shaping and supporting the inner wall of the stator before the step 2), the long groove is formed by laser cutting or mechanical cutting, and the inner support member is extracted from the inside of the stator after the step 4) is completed. The setting of the internal stay part is very simple, namely prevents the deformation of stator.

Further, the groove depth of each long groove is equal, and the distance between the groove bottom surface and the inner wall of the corresponding stator is 1/6-1/2 of the wall thickness of the stator.

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

In addition, be formed with along the mounting groove that self length direction extends at the rotor tip, ultrasonic sensor has a plurality ofly and sets up in the mounting groove side by side, and the grid has a multiunit, and with ultrasonic sensor one-to-one, wherein every grid of group distributes side by side along the length direction of stator, and has formed 180/N's angle deviation in proper order between every adjacent two sets of grids, and N is the number of grid strip. Through the corresponding arrangement of a plurality of grids and ultrasonic sensors, more information can be acquired, and therefore the ultrasonic rotary encoder can accurately calculate the rotation angle and the rotation speed of the stator.

Preferably, each grating and one ultrasonic sensor form a set of information acquisition units, and the ultrasonic rotary encoder further comprises an information acquisition unit having a single grating, wherein an angular deviation of 180 °/N is also formed between the single grating and the adjacent grating, and N is the number of grating. Under the action of a single grating strip, each movement period can be easily seen, so that the ultrasonic rotary encoder can conveniently and accurately judge.

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

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, errors caused by the grids to ultrasonic echo detection are greatly reduced, 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.

Drawings

FIG. 1 is a schematic view (partially cut-away) of the structure of an ultrasonic rotary encoder of the present invention;

fig. 2a, 2b, 2c and 2d are schematic views of the corresponding states in step 1);

FIGS. 3a and 3b are schematic views of the corresponding states in step 2);

FIGS. 4a and 4b are schematic views of the corresponding states in step 3);

fig. 5a and 5b are schematic views of the corresponding states in step 4);

FIG. 6 is a schematic diagram of the structure of an ultrasonic rotary encoder (absolute encoder) of the present invention;

wherein: 1. a sensor section; 10. a stator; 11. a rotor; 110. a mounting groove; 12. an ultrasonic sensor; 13. grid strips; 2. A rotation transmission section; 20. a rotating part; 21. an information transmission unit; 3. a signal processing section; 4. an inner support member; 5. a separation sleeve; 6. a material layer; 7. a coating; s, grating area; f. a non-grid region; c. an elongated slot; q, information acquisition unit.

Description of the embodiments

The present invention will be described in detail with reference to the drawings and the detailed description, so that the above objects, features and advantages of the present invention can be more clearly understood. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be embodied in many other forms than described herein and similarly modified by those skilled in the art without departing from the spirit of the invention, whereby the 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", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present invention.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, the meaning of "plurality" means at least two, for example, two, three, etc., unless specifically defined otherwise.

In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly, through intermediaries, or both, may be in communication with each other or in interaction with each other, unless expressly defined otherwise. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

In the invention, unless expressly stated or limited otherwise, a first feature "up" or "down" a second feature may be the first and second features in direct contact, or the first and second features in indirect contact through an intervening medium. Moreover, a first feature being "above," "over" and "on" a second feature may be a first feature being directly above or obliquely above the second feature, or simply indicating that the first feature is level higher than the second feature. The first feature being "under", "below" and "beneath" the second feature may be the first feature being directly under or obliquely below the second feature, or simply indicating that the first feature is less level than the second feature.

It will be understood that when an element is referred to as being "fixed" or "disposed" on another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like are used herein for illustrative purposes only and are not meant to be the only embodiment.

As shown in fig. 1, the ultrasonic rotary encoder disclosed in this embodiment includes a sensor section 1, a rotary transmission section 2 (which may be a slip ring, a rotary transformer, a rotary capacitor, a rotary optical fiber coupler, or the like), and a signal processing section 3, wherein the rotary transmission section 2 includes a rotary section 20 that drives a shaft to be detected to rotate about its own axis direction, an information transmission section 21 that communicates with the sensor section 1 and the signal processing section 3, detection information obtained by the sensor section 1 is transmitted to the signal processing section 3 by the information transmission section 21, and the signal processing section 3 performs signal analysis to obtain measurement information.

The sensor part 1 comprises a stator 10 with a circular cross section and a straight pipe shape, a rotor 11 which is freely rotatably arranged in the stator 10 around the central line direction of the stator 10, an ultrasonic sensor 12 which is fixedly arranged at the end part of the rotor 11 extending into the stator 10, and a plurality of grid bars 13 which are uniformly distributed around the circumference of the stator 10, wherein echo signals formed by the grid bars 13 are stronger than echo signals formed by the side wall of the stator, grids are formed between two adjacent grid bars 13, the grids which are sequentially arranged form grids, and the ultrasonic sensor 13 is positioned in an ultrasonic echo detection area formed by the grids.

In this example, the stator 10 is a plastic member and the grid bars 13 are metal members.

Specifically, the rotor is a detected shaft, and the diameter of the rotor is larger than or equal to 0.3mm; the inner diameter of the stator is larger than or equal to 0.4mm, and the outer diameter of the stator is larger 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 grid forming process is as follows:

referring to fig. 2a to 2d (wherein fig. 2a is a front view and fig. 2b is a right view; fig. 2c is a front view and fig. 2d is a right view), 1) setting and supporting an inner support member 4 on an inner wall of a stator 10, then sleeving a separation sleeve 5 dividing the stator 10 into a grid region s and a non-grid region f on an outer circumference of the stator 10, and then coating a material layer 6 easily peeled from a surface of the stator on the outer circumference of the stator 10 of the grid region s;

2) A plurality of elongated grooves c (shown in a front view in conjunction with fig. 3 a) formed on a wall surface of the stator 10 and recessed inward from a surface of the material layer 6, wherein each of the elongated grooves c has a same cross section, is a circular arc segment (shown in a right view from a middle portion of the elongated groove in conjunction with fig. 3 b) centered around a center of the stator, is uniformly distributed around a circumferential direction of the stator, and extends in a length direction along the stator;

3) A coating 7 (see fig. 4a and 4b, wherein fig. 4a is a front view and fig. 4b is a right view from the middle of the elongated slot) with uniform thickness is formed on the slot surface of the elongated slot c and the surface of the material layer 6 where the elongated slot is not formed, wherein the echo signal formed by the coating 7 is stronger than the echo signal formed by the side wall of the stator 10;

4) The material layer 6 with the coating 7 formed on the surface thereof is peeled off from the surface of the stator 10 (as shown in fig. 5a and 5b in combination, wherein fig. 5a is a front view and fig. 5b is a right view from the middle of the elongated groove), and the inner support member 4 is drawn out from the inside of the stator 10, and at this time, the coating formed in each elongated groove c is a grating strip 13, one grating is formed between every two adjacent grating strips 13, and a plurality of gratings arranged in sequence form the grating.

In order to further facilitate the grid forming, the following means are also adopted in this example.

In step 1), the material layer is a water-soluble glue layer, so that once the grid is formed, the whole stator is placed in water, and the material layer on the surface of the stator is quickly removed by dissolving the material layer.

Of course, the stripping of the material layer can be conveniently implemented by adopting a corresponding means of stripping the adhesive layer which is insoluble in water, heating (or light irradiation to deglue the adhesive layer), the parylene film layer and the external force.

In step 2), machining refers to machining or laser machining, but it is worth noting that the groove depth of each elongated groove is equal, and the distance between the groove bottom surface and the corresponding stator inner wall is 3/5 of the stator wall thickness.

Preferably, in step 3), the coating is formed on the outer circumference 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 is equal, so that the echo intensity provided by each grating strip is equal.

In this example, the metal material is one of materials such as stainless steel, gold, and aluminum, and is formed in the elongated groove on the outer periphery of the stator by vapor deposition.

As shown in fig. 6, a plurality of mounting grooves 110 extending along the longitudinal direction of the rotor 11 are formed at the end of the rotor, the ultrasonic sensors 12 are arranged in the mounting grooves 110 side by side, the grids are in one-to-one correspondence with the ultrasonic sensors 12, the formed ultrasonic echo detection areas are distributed side by side along the longitudinal direction of the stator 10, an angle deviation of 180 °/N is formed between every two adjacent groups of grids, and N is the number of grid bars. Through the corresponding arrangement of a plurality of grids and ultrasonic sensors, more information can be acquired, and therefore the ultrasonic rotary encoder can accurately calculate the rotation angle and the rotation speed of the stator.

Each grating and one ultrasonic sensor 13 form a group of information acquisition units q, and the ultrasonic rotary encoder further comprises an information acquisition unit q with single grating strips, wherein an angle deviation of 180 degrees/N is formed between each grating strip 13 and the adjacent grating, and N is the number of grating strips. Under the action of a single grating strip, each movement period can be easily seen, so that the ultrasonic rotary encoder can conveniently and accurately judge.

Thus, in this example, the information acquisition unit q has three sets, i.e., 3-bit gray coding, i.e., absolute type encoder.

Also, the number of bits of gray coding can be increased by increasing the number of lines of the scale and the number of ultrasonic sensors, thereby increasing the resolution of the encoder.

In addition, taking an ultrasonic probe with a center frequency of 50MHz as an example, the transverse resolution of the ultrasonic probe is about 200um, and the size of the resolution determines that the minimum scale interval of grid bars on a stator cannot be smaller than the transverse resolution of the ultrasonic probe, so that the required strong and weak signals can be obtained.

Assuming a lateral resolution of λ, the angular resolution of the encoder is at most 360 °/λ. But we can increase the accuracy of the encoder by increasing the number of sensors.

In summary, in this embodiment, the sensor is designed by using the intensity of the reflected echoes of the ultrasonic waves encountering different reflectors, and the rotation speed and the position of the rotating object are measured by using the principle of rotation coding.

Meanwhile, the ultra-high frequency miniature ultrasonic sensor can be used for measuring the rotating speed and the position of a detected shaft with the diameter of the detected shaft being more than 0.3mm, so that the ultra-high frequency miniature ultrasonic sensor can be applied to the field of high-precision detection, such as in-vivo interventional medical imaging equipment, can effectively correct image distortion (NURD) and the like caused by rotational distortion, ensures the accuracy of images, and has very good advantages.

The detection process of this embodiment is as follows:

(1) The detected shaft is adopted to replace the rotor, a mounting groove is formed at the end part of the rotor, and ultrasonic sensors are correspondingly distributed in the mounting groove and are correspondingly positioned in an ultrasonic echo detection area formed by a plurality of grid bars;

(2) The method comprises the steps of starting a rotary transmission part and an ultrasonic sensor, and collecting ultrasonic echo signals under synchronous rotation of a detected shaft and the ultrasonic sensor, wherein when an emission surface of the ultrasonic sensor is parallel to a tangent line of each grating strip, the reflection echo intensity is maximum Amax, when the emission surface of the ultrasonic sensor is opposite to the middle position between two adjacent grating strips, the reflection echo intensity is weakest Amin, and when the emission surface of the ultrasonic sensor is at other positions, the reflection echo intensity is between Amax and Amin;

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

Meanwhile, in order to further improve the resolution of the encoder, in the step (1), three groups of information acquisition units may be arranged side by side to form three-bit gray codes, and of course, multiple groups of multi-bit gray codes arranged side by side may also be used for detection, so that the motion data of the detected shaft can be more accurately obtained.

The present invention has been described in detail with the purpose of enabling those skilled in the art to understand the contents of the present invention and to implement the same, but not to limit the scope of the present invention, and all equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of the present invention.

Claims

1. An ultrasonic rotary encoder, characterized in that: the ultrasonic rotary encoder comprises a sensor part, a rotary transmission part and a signal processing part, wherein the sensor part comprises a stator with a circular and straight-pipe-shaped cross section, a rotor which is arranged in the stator in a free rotation mode around the central line direction of the stator, an ultrasonic sensor which is fixedly arranged at the end part of the rotor extending into the stator, and a plurality of grating bars which are uniformly distributed around the circumference of the stator, wherein the echo signals formed by the grating bars and the echo signals formed by the side wall of the stator have strong and weak differences, each two adjacent grating bars form a grating, the gratings are sequentially arranged to form a plurality of groups, each group of gratings are distributed along the length direction of the stator, each two adjacent groups of gratings are sequentially formed with an angle deviation of 180 DEG/N, N is the number of the grating bars, the ultrasonic sensor is a plurality of ultrasonic echo detection areas formed by the gratings, one group of gratings and one ultrasonic sensor form one group of information acquisition units, each group of information acquisition units has a single grating bar, and the lambda meter has a lambda meter with the highest angle resolution of 360 degrees.

2. An ultrasonic rotary encoder according to claim 1, wherein: an angle deviation of 180 degrees/N is formed between each grid bar and the adjacent grids of the grids, and N is the number of the grid bars.

3. An ultrasonic rotary encoder according to claim 1, wherein: the grating strip forms an echo signal that is stronger than an echo signal formed by the stator sidewall.

4. An ultrasonic rotary encoder according to claim 3, wherein: the stator is made of plastic or rubber, and the grid strips are formed by a metal coating or are metal pieces.

5. An ultrasonic rotary encoder according to claim 1, wherein: the grid strip is characterized in that a plurality of long grooves are formed in the stator, each long groove is an arc section taking the center of the stator as the center of a circle, each long groove extends along the length direction of the stator, the grid strips are in one-to-one correspondence with the long grooves, and the grid strips are arranged in the long grooves.

6. An ultrasonic rotary encoder according to claim 5, wherein: the long grooves are positioned on the outer wall surface of the stator, the groove depth of each long groove is equal, and the distance between the groove bottom surface and the inner wall of the corresponding stator is 1/6-1/2 of the wall thickness of the stator.

7. An ultrasonic rotary encoder according to claim 6, wherein: the grid strips are metal coatings formed in the long grooves through spraying, vapor plating or sputtering, and the thickness of the grid strips is equal to the groove depth of the corresponding long grooves.

8. An ultrasonic rotary encoder according to claim 1, wherein: the rotor is a detected shaft, and the diameter of the rotor is larger than or equal to 0.3mm; the inner diameter of the stator is larger than or equal to 0.4mm, and the outer diameter of the stator is larger than or equal to 0.5mm.

9. An ultrasonic rotary encoder according to claim 1, wherein: the rotor end portion is formed with a mounting groove extending in a longitudinal direction thereof, and the plurality of ultrasonic sensors are arranged in the mounting groove in parallel.

10. An ultrasonic rotary encoder according to claim 1, wherein: the grid forming process comprises the following steps:

1) Uniformly coating a material layer which is easy to peel off from the surface of the stator on the inner wall or the periphery of the stator and corresponding to the position of the ultrasonic sensor, wherein the material layer is a glue layer which can be dissolved in water, a glue layer which cannot be dissolved in water or a film layer;

2) A plurality of long grooves which are concavely processed inwards from the surface of the material layer and are formed on the wall surface of the stator, wherein the section of each long groove is the same, each long groove takes the center of the stator as an arc section of the circle center, the plurality of long grooves are uniformly distributed around the circumference of the stator, and each long groove extends along the length direction of the stator;

3) Forming a coating with consistent thickness on the groove surface of the long groove and the surface of the material layer, wherein the echo signals formed by the coating and the echo signals formed by the side wall of the stator have strong and weak differences;

4) And stripping the material layer with the coating formed on the surface from the surface of the stator, wherein the stripping means is dissolution, heating, illumination or external force stripping, the coating formed in each long groove is a grid strip, one grid is formed between every two adjacent grid strips, and a plurality of grids which are sequentially arranged form the grid.