Self-focusing ultrasonic transducer, sweeping robot and acoustic impedance calculation method

Abstract

The application discloses a self-focusing ultrasonic transducer, a sweeping robot and an acoustic impedance calculation method, and relates to the technical field of self-focusing ultrasonic transducers.The self-focusing ultrasonic transducer comprises a support, the bottom of the support is provided with a concave spherical surface, the periphery of the concave spherical surface is provided with an annular plane, the upper end of the support is provided with a connecting joint; a cross-linked polypropylene piezoelectric electret film, the upper and lower surfaces of the cross-linked polypropylene piezoelectric electret film are printed with conductive silver paste and covered in the concave spherical surface; a shielding wire, one end of the shielding wire is connected with the lower surface edge of the cross-linked polypropylene piezoelectric electret film, and the other end is connected with the connecting joint and used as a positive electrode; a silver film, the silver layer is plated on the surface of the support, the upper surface of the cross-linked polypropylene piezoelectric electret film is connected with the connecting joint and used as a negative electrode. The self-focusing ultrasonic transducer can realize self-focusing of acoustic energy, and can identify and detect the acoustic resistance of a reflected object, identify different materials of the reflected object, and control the robot to switch different working modes according to different materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sweeping robots, in particular to a self-focusing ultrasonic transducer, a sweeping robot and an acoustic impedance calculation method. BACKGROUND

[0002] Sweeping robots are increasingly popular in society due to their efficient and intelligent cleaning methods. Sweeping robots generally use brushing and vacuuming methods to first absorb the ground debris into their own garbage collection box, thereby completing the function of ground cleaning. In addition, some sweeping robots are equipped with a water tank and can complete the function of wiping the floor. When sweeping, if a carpet is encountered, the sweeping robot will change its walking path to avoid damaging the carpet. Therefore, it is necessary to detect the carpet and other ground materials.

[0003] Currently, in the prior art, the carpet detection method of the sweeping robot is to determine whether there is a carpet according to the change of the working current of the brush roll or the motor or the internal sound characteristics. Patents ZL201610765425.0 and ZL201910172819.9 propose that when the sweeping robot is on a carpet material, the working current of the brush roll or the motor will increase, and the carpet and non-carpet conditions are determined by monitoring the current. Patent ZL201810645504.7 proposes to collect the sound generated inside the motor and reflected by the ground for analysis to determine the ground material. However, when the sweeping robot is subjected to resistance from non-carpet materials (such as hair entanglement, side brush obstruction, obstacle crossing, etc.), it will cause sound changes and lead to misjudgment.

[0004] Therefore, the air-coupled ultrasonic transducer provides a solution to such problems. Existing research on air-coupled ultrasonic transducers, such as patent ZL201721476404.3, provides a structure of a self-focusing ultrasonic transducer, but the patent uses a piezoelectric ceramic wafer as a vibration element, which has a narrow bandwidth and is a fragile material that needs to be finely processed to make a curved surface to achieve focusing. Patent ZL201811191335.0 provides a point-focusing air-coupled ultrasonic transducer structure, which uses a porous polypropylene ferroelectric electret film as a vibration element and is attached to an arc-shaped metal backing to achieve focusing. However, the arc-shaped surface of the metal backing is made by fine machining on a machine tool, which is difficult to produce and cannot be designed.

[0005] Therefore, in order to achieve detection of ground materials, ensure detection accuracy and improve detection efficiency, it is necessary to develop a self-focusing ultrasonic transducer and a sweeping robot. SUMMARY

[0006] In view of the deficiencies of the prior art, one of the purposes of the present application is to provide a self-focusing ultrasonic transducer with a reasonable structure that can be assembled at the bottom of a sweeping robot. The technical scheme adopted is as follows:

[0007] A self-focusing ultrasonic transducer comprises:

[0008] A support, the bottom of which is provided with a concave spherical surface, the periphery of which is surrounded by an annular plane, and the upper end of which is provided with a connecting joint;

[0009] A cross-linked polypropylene piezoelectric electret film, the upper and lower surfaces of which are printed with conductive silver paste and covered in the concave spherical surface;

[0010] A shielding wire, one end of which is connected to the lower surface edge of the cross-linked polypropylene piezoelectric electret film, and the other end of which is connected to the connecting joint as a positive electrode;

[0011] A silver film, the silver layer of which is plated on the surface of the support, and the upper surface of the cross-linked polypropylene piezoelectric electret film is connected to the connecting joint as a negative electrode.

[0012] As a further improvement of the present application, the side wall of the support is provided with a fixing slot, and the shielding wire is fixed in the fixing slot.

[0013] As a further improvement of the present application, the support is cylindrical in shape, the radius of the support is 6 mm, and the height is 20 mm.

[0014] As a further improvement of the present application, the radius of curvature of the concave spherical surface is 10 mm, and the opening radius is 4 mm.

[0015] As a further improvement of the present application, the top of the support is provided with a fixing cavity for fixing the connecting joint.

[0016] As a further improvement of the present application, the connecting joint is fixed in the fixing cavity by epoxy glue.

[0017] As a further improvement of the present application, the inside of the support is provided with a hollow cavity in communication with the fixing cavity.

[0018] As a further improvement of the present application, the connecting joint is a BNC joint or an SMA joint.

[0019] The second object of the present application is to provide a sweeping robot, which comprises the following technical solutions:

[0020] A sweeping robot comprises a body, the bottom of which is provided with the self-focusing ultrasonic transducer described above.

[0021] The third object of the present application is to provide a method for calculating acoustic impedance, which comprises the following technical solutions:

[0022] A method for calculating acoustic impedance, applied to the self-focusing ultrasonic transducer as claimed in any one of claims 1-8, characterized in that it comprises the following steps:

[0023] S10, converting the collected time-amplitude signal into a distance-amplitude signal, selecting i distance intervals, and taking the maximum value A of the echo in the interval i and the corresponding propagation distance d i ;

[0024] S20, performing exponential fitting on A i and d i to obtain the ultrasonic attenuation formula y=A·e -β·d =A·r·e -α·d , and obtain the acoustic pressure reflection coefficient r=e (α-β)·d ; wherein y is the ultrasonic attenuation coefficient, β is the attenuation coefficient obtained by fitting, d is the distance difference between two echoes, r is a dimensionless unit, and α is the attenuation coefficient of air at the excitation frequency of the transducer;

[0025] S30, obtaining from the acoustic pressure reflection coefficient formula ; wherein Z1 is the acoustic impedance of air, and Z2 is the acoustic impedance of the reflecting object.

[0026] The beneficial effects of the present application are:

[0027] The self-focusing ultrasonic transducer can be assembled at the bottom of the sweeping robot, can realize self-focusing of acoustic energy, and can identify and detect the acoustic impedance of the reflecting object, identify different materials of the reflecting object, and control the robot to switch different working modes according to different materials.

[0028] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the content of the specification can be implemented, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following preferred embodiments are described in detail, and the accompanying drawings are as follows. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structural schematic diagram of the self-focusing ultrasonic transducer in the preferred embodiment of the present application;

[0030] Figure 2 is a structural schematic diagram of the support in the preferred embodiment of the present application;

[0031] Figure 3 is a structural schematic diagram of the sweeping robot in the preferred embodiment of the present application;

[0032] Figure 4 is a signal transmission schematic diagram of the ultrasonic transducer in the preferred embodiment of the present application;

[0033] Figure 5 This is a flowchart of the acoustic impedance calculation method in a preferred embodiment of the present invention;

[0034] Figure 6(af) is a schematic diagram of the reflected signals collected at 20 mm on different materials by the self-focusing ultrasonic transducer in a preferred embodiment of the present invention.

[0035] Marking descriptions: 10, support component; 11, concave spherical surface; 12, annular plane; 13, fixed cavity; 14, hollow cavity; 20, connecting joint; 30, cross-linked polypropylene piezoelectric electret film; 40, shielding wire; 50, silver film; 100, self-focusing ultrasonic transducer; 200, body. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0037] like Figure 1 As shown, this is a self-focusing ultrasonic transducer in an embodiment of the present invention, which includes a support member 10, a cross-linked polypropylene piezoelectric electret film 30, a shielding wire 40 and a silver film 50, and a connecting joint 20 is provided at the upper end of the support member 10.

[0038] like Figure 2 As shown, the bottom of the support member 10 is provided with a concave spherical surface 11, and an annular plane 12 is provided around the concave spherical surface 11.

[0039] like Figure 1 As shown, conductive silver paste is printed on both the upper and lower surfaces of the cross-linked polypropylene piezoelectric electret film 30 and covers the concave spherical surface 11. One end of the shielding wire 40 is connected to the lower surface edge of the cross-linked polypropylene piezoelectric electret film 30, and the other end is connected to the connector 20 as the positive electrode. The silver layer is plated on the surface of the support 10, and the upper surface of the cross-linked polypropylene piezoelectric electret film 30 is connected to the connector 20 as the negative electrode.

[0040] In one embodiment, the side wall of the support member 10 is provided with a fixing seam, and the shielding wire 40 is fixed in the fixing seam to prevent short circuit.

[0041] In one embodiment, the support member 10 is cylindrical in shape, with a radius of 6 mm and a height of 20 mm. The concave spherical surface 11 has a radius of curvature of 10 mm and an opening radius of 4 mm. In other embodiments of the invention, the dimensions of the support member 10 and the concave spherical surface 11 can be set as needed.

[0042] In the embodiment, the top of the support 10 is provided with a fixed cavity 13 for fixing the connecting joint 20, and the connecting joint 20 is fixed in the fixed cavity 13 by epoxy glue. The structure stability can be improved.

[0043] In the embodiment, the support 10 is internally provided with a hollow cavity 14 in communication with the fixed cavity 13, which is beneficial to reduce the weight and save the cost.

[0044] Preferably, the connecting joint 20 is a BNC joint or an SMA joint.

[0045] In the embodiment, the support 10 is a 3D printed part.

[0046] As shown in Figure 3 , the self-focusing ultrasonic transducer 100 is assembled on the bottom of the body 200 of the sweeping robot in the embodiment, and the body 200 is internally provided with an ultrasonic transceiving module and a microprocessor. Figure 4 As shown in , the microprocessor is connected with the ultrasonic transceiving module and sends a driving signal, the ultrasonic transceiving module converts the driving signal into a 100V high-voltage sharp pulse and transmits the pulse to the self-focusing ultrasonic transducer 100 through the connecting joint 20. The self-focusing ultrasonic transducer 100 excites and receives the reflected echo of the ground. The echo is received and amplified by the ultrasonic transceiving module and then transmitted back to the microprocessor for subsequent signal processing.

[0047] Figure 5 The above signal processing includes calculating the acoustic impedance of the reflection object, as shown in

[0048] S10, converting the collected time-amplitude signal into a distance-amplitude signal, selecting i distance intervals, and taking the maximum value A of the echo in the interval i and the corresponding propagation distance d i ; specifically, the collected time-amplitude signal is converted into a distance-amplitude signal by the formula d=v·t, where d is the distance, the unit is m; v is the environmental sound speed, the unit is m / s; t is the time, the unit is s.

[0049] S20, exponential fitting is performed on A i and d i , to obtain an ultrasonic attenuation formula y=A·e -β·d =A·r·e -α·d , and an acoustic pressure reflection coefficient r=e (α-β)·d ; wherein y is the ultrasonic attenuation coefficient, β is the attenuation coefficient obtained by fitting, the unit is db / mm; d is the distance difference between two echoes, the unit is mm; r is a dimensionless unit; α is the attenuation coefficient of air at the transducer excitation frequency, which is 0.0016 db / mm in the embodiment.

[0050] S30, according to the sound pressure reflection coefficient formula obtained Wherein, Z1 is air acoustic impedance, 416 Rayl in the embodiment, Z2 is the reflected object acoustic impedance. In the embodiment, the acoustic impedance of the ceramic tile, the ceramic tile with water stains, the wooden floor, the wooden floor with water stains, and the short carpet is calculated as shown in Table 1.

[0051]

[0052] Table 1

[0053] Fig. 6 (a-f) is a schematic diagram of the reflected signal collected by the self-focusing ultrasonic transducer at 20 mm on different materials in the preferred embodiment of the application. From Figure 6a to 6f are the ceramic tile, the ceramic tile with water stains, the wooden floor, the wooden floor with water stains, the short carpet and the long carpet, wherein, since the long carpet has only one reflection echo, data fitting cannot be performed, so its acoustic impedance cannot be calculated, but it can be identified by the number of echoes.

[0054] To avoid errors, the acoustic resistance range is set in the microprocessor and the function of the control module is adjusted. When there is only one echo and the acoustic impedance cannot be calculated, it is determined to be a long carpet, the direction of the floor cleaning robot is changed to avoid damage caused by the long carpet; when Z2<3000, it is determined to be a short carpet, the scrubbing function is turned off, and the suction force is increased to effectively clean the debris in the short carpet; when 3000≤Z2<4500, it is determined to be a wooden floor, and the default working mode is switched; when R2≥4500, it is determined to be a ceramic tile or there are water stains on the ground, and the water tank is controlled to output water at a rate of 2 ml / s to avoid leaving a large amount of water stains on the ground to cause wetness.

[0055] The self-focusing ultrasonic transducer of the application can be assembled at the bottom of the floor cleaning robot, can realize self-focusing of acoustic energy, and can identify and detect the acoustic resistance of the reflected object, identify different materials of the reflected object, and control the robot to switch different working modes according to different materials.

[0056] The above embodiments are only preferred embodiments for fully illustrating the application, and the protection scope of the application is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the application are within the protection scope of the application. The protection scope of the application is subject to the claims.

Claims

1. A self-focusing ultrasonic transducer, characterized by, It comprises: a support, the bottom of which is provided with a concave spherical surface, the periphery of which is surrounded by an annular plane, and the upper end of which is provided with a connecting joint; a cross-linked polypropylene piezoelectric electret film, the upper and lower surfaces of which are printed with conductive silver paste and covered in the concave spherical surface; a shield wire, one end of which is connected to the lower surface edge of the cross-linked polypropylene piezoelectric electret film, and the other end of which is connected to the connecting joint as a positive electrode; a silver film, which is plated on the surface of the support, and connects the upper surface of the cross-linked polypropylene piezoelectric electret film to the connecting joint as a negative electrode; the side wall of the support is provided with a fixing slot, and the shield wire is fixed in the fixing slot; the support is in the shape of a cylinder, the radius of the support is 6 mm, and the height is 20 mm; the top of the support is provided with a fixing cavity for fixing the connecting joint.

2. The self-focusing ultrasonic transducer of claim 1, wherein, The radius of curvature of the concave spherical surface is 10 mm, and the opening radius is 4 mm.

3. The self-focusing ultrasonic transducer of claim 1, wherein, The connecting joint is fixed in the fixing cavity by epoxy glue.

4. The self-focusing ultrasonic transducer of claim 1, wherein, The inside of the support is provided with a hollow cavity in communication with the fixing cavity.

5. The self-focusing ultrasonic transducer of claim 1, wherein, The connecting joint is a BNC joint or an SMA joint.

6. A robotic vacuum cleaner comprising a body, characterised in that, The body is equipped with a self-focusing ultrasonic transducer as claimed in any one of claims 1-5.

7. An acoustic impedance calculation method, characterized by, The self-focusing ultrasonic transducer as claimed in any one of claims 1-6, characterized in that it comprises the following steps: S10, converting the time-amplitude signal collected into a distance-amplitude signal, selecting i distance intervals, and taking the maximum value A of the echo in the interval i corresponding to the propagation distance d i ; S20, to A i and d i Exponential fitting is performed to obtain the ultrasonic attenuation formula and the sound pressure reflection coefficient ; wherein y is the ultrasonic attenuation coefficient, β is the attenuation coefficient obtained by fitting, d is the distance difference between two echoes, r is a dimensionless unit, and α is the attenuation coefficient of air at the excitation frequency of the transducer. S30, according to the sound pressure reflection coefficient formula obtained ; wherein Z1 is the air acoustic impedance, and Z2 is the reflected object acoustic impedance.

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