MANUAL ACOUSTIC AXIS ALIGNING METHOD FOR ULTRASONIC SOUND FIELD MEASURING SYSTEM

Abstract

The present disclosure belongs to the technical field of an ultrasonic sound field measuring system, and relates to a manual acoustic axis aligning method for an ultrasonic sound field measuring system. The method comprises: obtaining an intersection between a current acoustic axis and a plane by scanning two detection planes, and calculating an inclination angle of the current acoustic axis; judging whether the inclination angle is less than an adjustment threshold. The method does not depend on the specific mechanical implementation of adjusting an acoustic axis angle. The iterative algorithm combined with geometric information can converge quickly. The criterion of intersection between the acoustic axis and the plane used is not limited to the amplitude criterion, and other criteria can be introduced by increasing the distance between two planes to increase the robustness of measuring the acoustic axis angle.

Claims

1. A manual acoustic axis aligning method for an ultrasonic sound field measuring system, specifically comprising the following cycles: 1) determining three planes according to the focus position, wherein the three planes are a focusing plane Z.sub.focus, an acoustic axis angle detection plane Z.sub.1 and an acoustic axis angle detection plane Z.sub.2; defining the distances from the probe surface to the focusing plane Z.sub.focus, the acoustic axis angle detection plane Z.sub.1 and the acoustic axis angle detection plane Z.sub.2 as D.sub.focus, a and b, respectively; 2) determining a peak point of an underwater acoustic signal of the focusing plane Z.sub.focus and taking the peak point as an initial center point PC.sub.i, and denoting the coordinate of the initial center point PC.sub.1 as [PC_X.sub.1, PC_Y.sub.1]; 3) in the acoustic axis angle detection plane Z.sub.1, scanning with PC.sub.i as the center, changing the coordinates of X and Y, and acquiring sound field signals to obtain the intersection C1=[C1.sub.X, C1.sub.Y] between the acoustic axis and the acoustic axis angle detection plane Z.sub.1, where i is a positive integer; 4) in the acoustic axis angle detection plane Z.sub.2, scanning with PC.sub.i as the center, changing the coordinates of X and Y, and acquiring sound field signals to obtain the intersection C2=[C2.sub.X, C2.sub.Y] between the acoustic axis and the acoustic axis angle detection plane Z.sub.2, where i is a positive integer; 5) calculating the inclination angle θ.sub.i=[θx.sub.i, θy.sub.i] of the current acoustic axis according to the intersection points C1 and C2; θx.sub.i is the included angle between the acoustic axis and Z axis after the acoustic axis is projected on XOZ plane, and θy.sub.i is the included angle between the acoustic axis and Z axis after the acoustic axis is projected on YOZ plane; 6) judging whether the inclination angle θ.sub.i is less than the adjustment threshold, if so, aligning the acoustic axis, ending the adjustment, otherwise, proceeding to step 7); 7) according to the inclination angle θ.sub.i, calculating the next coordinate PC; [PC_X.sub.i, PC_Y.sub.i] by using an iterative algorithm where i is an integer not less than 2; 8) keeping PC.sub.i of the X axis and Y axis unchanged, moving the Z axis to the focusing plane Z.sub.focus, manually adjusting two corner adjustment knobs of a probe clamping device until the amplitude of a hydrophone measurement signal at the current coordinate point is the maximum, and then proceeding to step 3).

2. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein in step 1), the acoustic axis angle detection plane Z.sub.1 and the acoustic axis angle detection plane Z.sub.2 are located on the same side or different sides of the focusing plane Z.sub.focus.

3. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein in step 2), the peak point is the maximum point of the underwater acoustic signal of the focusing plane.

4. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein in step 3) and step 4), according to the acquired sound field signals, the intersection C1==[C1.sub.X, C1.sub.Y] between the acoustic axis and the acoustic axis angle detection plane Z.sub.1, and the intersection C2=[C2.sub.X, C2.sub.Y] between the acoustic axis and the acoustic axis angle detection plane Z.sub.2 are obtained by a simple amplitude criterion or the criterion for calculating the symmetry center based on symmetry, respectively.

5. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 4, wherein the simple amplitude criterion is the amplitude maximum criterion, and the criterion for calculating the symmetry center based on symmetry is the centroid criterion.

6. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein in step 5), the specific calculation formula of the coordinate value of the inclination angle θ.sub.i is as follows:
θx.sub.i=arcctan((C2.sub.X−C1.sub.X)/(b−a))  (1)
θy.sub.i=arcctan((C2.sub.Y−C1.sub.Y)/(b−a))  (2).

7. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein in step 7), calculating the next coordinate PC.sub.i=[PCX.sub.i, PC_Y.sub.i] by using an iterative algorithm has the specific calculation process as follows: if the inclination angle of the current acoustic axis is obtained after the first adjustment, calculating the adjustment amount according to the triangular relationship, the coordinate PC.sub.2=[PC_X.sub.2, PC_Y.sub.2] of a new center point is calculated according to the depth D.sub.focus of the focusing plane Z.sub.focus with the following formula:
PC_X.sub.2=PC_X.sub.1+tan(θx.sub.1)×(D.sub.focus−a)  (3)
PC_Y.sub.2=PC_Y.sub.1+tan(θy.sub.1)×(D.sub.focus−a)  (4) in the above formulas (3) and (4), the inclination angle θ.sub.1=[θx.sub.1, θy.sub.1] of the current acoustic axis is obtained after the first adjustment; otherwise, the calculation formula of the coordinate PC.sub.i+1=[PC_X.sub.i+1, PC_Y.sub.i+1] of the new center point is as follows:
PC_X.sub.i+1=(PC_X.sub.i−PC_X.sub.i−1)/(θx.sub.i−θx.sub.i−1)×θx.sub.i  (5)
PC_Y.sub.i+1=(PC_Y.sub.i−PC_Y.sub.i−1)/(θy.sub.i−θy.sub.i−1)×θy.sub.i  (6) in the above formulas (5) and (6), i is an integer not less than 2, the inclination angle of the current acoustic axis is θ.sub.i=[θx.sub.i, θy.sub.i], and the inclination angle before the inclination angle of the current acoustic axis is adjusted is θ.sub.i−1=[θx.sub.i−1, θy.sub.i−1].

8. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein the order of step 3) and the order of step 4) are interchangeable.

9. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein in step 3) and step 4), a computer controls a water tank system to automatically scan the acoustic axis angle detection plane Z.sub.1 or the acoustic axis angle detection plane Z.sub.2.

10. The manual acoustic axis aligning method for an ultrasonic sound field measuring system according to claim 1, wherein the larger the interval between the acoustic axis angle detection plane Z.sub.1 and the acoustic axis angle detection plane Z.sub.2, the higher the alignment accuracy.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a schematic structural diagram of a multi-axis water tank system.

[0032] FIG. 2 is a schematic structural diagram of a device of adjusting an acoustic axis angle using two manual axes.

[0033] FIG. 3(a) is a schematic diagram of acoustic axis angle detection planes Z.sub.1 and Z.sub.2 located at the upper side of a focusing plane Z.sub.focus according to the present disclosure.

[0034] FIG. 3(b) is a schematic diagram of acoustic axis angle detection planes Z.sub.1 and Z.sub.2 located at the lower side of a focusing plane Z.sub.focus according to the present disclosure.

[0035] FIG. 3(c) is a schematic diagram of acoustic axis angle detection planes Z.sub.1 and Z.sub.2 located at both sides of a focusing plane Z.sub.focus according to the present disclosure.

[0036] FIG. 4 is a graph showing the change of the current deviation angle of a manual acoustic axis aligning method in XOZ, plane with the number of iterations according to the present disclosure.

[0037] FIG. 5 is a graph showing the change of a single adjustment amount of a manual acoustic axis aligning method in XOZ plane with the number of iterations according to the present disclosure.

[0038] FIG. 6 is a graph showing the change of the current deviation angle of a manual acoustic axis aligning method in YOZ plane with the number of iterations according to the present disclosure.

[0039] FIG. 7 is a graph showing the change of a single adjustment amount of a manual acoustic axis aligning method in YOZ plane with the number of iterations according to the present disclosure.

[0040] FIG. 8 is a flowchart of a manual acoustic axis aligning method according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present disclosure will be further described in detail with reference to the drawings hereinafter.

[0042] As shown in FIG. 8, the present disclosure provides a manual acoustic axis aligning method for an ultrasonic sound field measuring system, specifically comprising the following cycles:

[0043] S1, determining three planes according to the focus position, wherein the three planes are a focusing plane Z.sub.focus, an acoustic axis angle detection plane Z.sub.1 and an acoustic axis angle detection plane Z.sub.2; defining the distances from the probe surface to the focusing plane Z.sub.focus, the acoustic axis angle detection plane Z.sub.1 and the acoustic axis angle detection plane Z.sub.2 as D.sub.focus, a and b, respectively; for convenience of description, FIGS. 3(a), (b) and (c) show the acoustic axis angle detection planes Z.sub.1 and Z.sub.2, the focusing plane Z.sub.focus and the projection of the acoustic axis on XOZ plane, with similar results in YOZ plane: D.sub.focus is the focal depth of the probe, which is determined by the probe parameters; the acoustic angle detection planes Z.sub.1, Z.sub.2 can be located at the upper side of the focusing plane Z.sub.focus (i.e. in front of the focusing plane), as shown in FIG. 3 (a); or located at the lower side of the focusing plane Z.sub.focus (i.e. behind the focusing plane), as shown in FIG. 3 (b); or at both sides of the focusing plane Z.sub.focus, as shown in FIG. 3 (c); the larger the interval between the acoustic angle detection planes Z.sub.1 and Z.sub.2, the more accurate the angle measurement and the higher the alignment accuracy;

[0044] S2, determining a peak point of an underwater acoustic signal of the focusing plane Z.sub.focus> and taking the peak point as an initial center point PC.sub.1, and denoting the coordinate of the initial center point PC.sub.1 as [PC_X.sub.1, PC_Y.sub.1]; wherein the peak point is the maximum point, of the underwater acoustic signal of the focusing plane;

[0045] S3, scanning the Z.sub.1 plane: in the Z.sub.1 plane, scanning with PC.sub.i as the center, changing the coordinates of X and Y, and acquiring sound field signals to obtain the intersection C1=[C1.sub.X, C1.sub.Y] between the acoustic axis and the Z.sub.1 plane through the criteria, such as centroid or maximum value;

[0046] S4, scanning the Z.sub.2 plane: in the Z.sub.2 plane, scanning with PC.sub.i as the center, changing the coordinates of X and Y, and acquiring sound field signals to obtain the intersection C2=[C2.sub.X, C1.sub.Y] between the acoustic axis and the Z.sub.2 plane through the criteria such as centroid or maximum value;

[0047] S5, calculating the inclination angle θ.sub.i=[θx.sub.i, θy.sub.i] of the current acoustic axis according to the intersection points C1 and C2; wherein θx.sub.i is the included angle between the acoustic axis and Z axis after the acoustic axis is projected on XOZ plane, and θy.sub.i is the included angle between the acoustic axis and Z axis after the acoustic axis is projected on YOZ plane;

θx.sub.i=arcctan((C2.sub.X−C1.sub.X)/(b−a))  (1)

θy.sub.i=arcctan((C2.sub.Y−C1.sub.Y)/(b−a))  (2)

[0048] S6, determining an adjustment threshold according to the alignment accuracy requirement of sound field measurement, and judging whether the current inclination angle θ.sub.i is smaller than the adjustment threshold; if so, aligning the acoustic axis, ending the adjustment, otherwise, proceeding to step S7;

[0049] S7, according to the inclination angle θ.sub.i, calculating the next coordinate PC.sub.i=[PC_X.sub.i, PC_Y.sub.i] by using an iterative algorithm, and the specific calculation process is as follows:

[0050] setting the inclination angle θ.sub.i=[θx.sub.i, θy.sub.i] of the current acoustic axis, and the result after iteration is as follows:

[0051] if the inclination angle of the current acoustic axis is obtained after the first adjustment, calculating the adjustment amount according to the triangular relationship, the coordinate PC.sub.2=[PC_X.sub.2, PC_Y.sub.2] of a new center point is calculated according to the depth. D.sub.focus of the focusing plane Z.sub.focus with the following formula:

PC_X.sub.2=PC_X.sub.1+tan(θx.sub.1)×(D.sub.focus−a)  (3)

PC_Y.sub.2=PC_Y.sub.1+tan(θy.sub.1)×(D.sub.focus−a)  (4)

[0052] if the inclination angle of the current acoustic axis is not obtained after the first adjustment, the calculation formula of the coordinate PC.sub.2=[PC_X.sub.2, PC_Y.sub.2] of the new center point is as follows:

PC_X.sub.i+1=(PC_X.sub.i−PC_X.sub.i−1)/(θx.sub.i−θx.sub.i−1)×θx.sub.i  (5)

PC_Y.sub.i+1=(PC_Y.sub.i−PC_Y.sub.i−1)/(θy.sub.i−θy.sub.i−1)×θy.sub.i  (6)

[0053] in the above formulas (5) and (6), i is an integer not less than 2, the inclination angle of the current acoustic axis is θ.sub.i=[θx.sub.i, θy.sub.i], and the inclination angle before the inclination angle of the current acoustic axis is adjusted is θ.sub.i−1=[θx.sub.i−1, θy.sub.i−1];

[0054] S8, keeping PC.sub.i of the X axis and Y axis unchanged, moving the Z axis to the focusing plane Z.sub.focus, manually adjusting two corner adjustment knobs of a probe clamping device until the amplitude of a hydrophone measurement signal at the current coordinate point is the maximum, and then proceeding to step S3.

[0055] Further, the position of the intersection of the acoustic axis can be judged and calculated according to the acquired sound field signal. The specific criterion can be a simple amplitude criterion or other criteria for calculating the symmetry center based on symmetry. Considering that the criterion based on amplitude (maximum amplitude) can only be used around the focusing plane, the criterion is invalid when being far away from the focusing plane (the signal amplitude on the acoustic axis is no longer the maximum value of the XOY plane). The criterion of intersection between the acoustic axis and the plane used in the present disclosure is not limited to the amplitude criterion, and other criteria can be introduced by increasing the distance between two planes to increase the robustness of measuring the acoustic axis angle. Since the acoustic axis angle measurement is a control parameter that affects the next iteration, the increase of the measurement robustness will enhance the robustness of the whole, iteration process.

[0056] Further, in S3 and S4, the computer controls the water tank system to automatically scan the current plane.

[0057] Further, the order of step S3 and the order of step S4 are interchangeable. When the order of S3 and the order of S4 are exchanged, correspondingly, S8 is performed, keeping PC.sub.i of the X axis and Y axis unchanged, moving the Z axis to the focusing plane Z.sub.focus, manually adjusting two corner adjustment knobs of a probe clamping device until the amplitude of a hydrophone measurement signal at the current coordinate point is the maximum, and then proceeding to step S3, that is, the exchanged step S4.

[0058] To sum up, the method can quickly and effectively realize the manual acoustic axis accurate alignment.

Embodiment

[0059] A specific implementation process of aligning the acoustic axis using this method is given hereinafter, specifically comprising the following cycles:

[0060] S1, determining three planes Z.sub.focus, Z.sub.1 and Z.sub.2 according to the focus position, wherein D.sub.focus is 13.3 cm, Z.sub.1 and Z.sub.2 are taken as the two planes at the upper side of the focus, and the corresponding distances a=2.8 cm and b=10.8 cm;

[0061] S2, finding a peak point of an underwater acoustic signal on the focusing plane Z.sub.focus, and taking the peak point as an initial center point Pei, in which the value of the coordinate [PC_X.sub.1, PC_Y.sub.1] is [−8.18, −7.48] cm;

[0062] S3, in the Z.sub.1 plane, taking PC.sub.1 as the center, carrying out two-dimensional scanning in the range of [−5, 5] cm from the center, in X direction and in the range of [−5, 5] cm from the center in Y direction;

[0063] the specific process is as follows: setting the moving range of Y direction to move from −5 cm to 5 cm away from the center, for each value of Y, moving from −5 cm to 5 cm away from the center in X direction, recording the waveform point by point, then adding Y, and then moving in X direction of the next line; after moving in the range of Y direction, counting the maximum amplitude value of the received signal at each position point, and calculating the centroid position of the whole scanning plane according to the maximum amplitude value, in which the centroid position is C1=[C1.sub.X, C1.sub.Y]=[−9.02, −8.75] cm;

[0064] S4, in the Z.sub.2 plane, taking PC.sub.2 as the center, carrying out two-dimensional scanning in the range of [−5, 5] cm from the center in X direction and in the range of [−5, 5] cm from the center in Y direction; the specific process is as follows: setting the moving range of Y direction to move from −5 cm to 5 cm away from the center, for each value of Y, moving from −5 cm to 5 cm away from the center in X direction, recording the waveform point by point, then adding Y, and then moving in X direction of the next fine; after moving in the range of Y direction, counting the maximum amplitude value of the received signal at each position point, and calculating the centroid position of the whole scanning plane according to the maximum amplitude value, in which the centroid position is C2=[C2.sub.X, C1.sub.Y]=[−8.38, −7.78] cm;

[0065] S5, calculating the inclination angle θ.sub.i=[θx.sub.i, θy.sub.i]=[4.57°, 6.91° ] of the current acoustic axis according to the intersection points C1 and C2; where θx.sub.i is the included angle between the acoustic axis and Z axis after the acoustic axis is projected on XOZ plane, sand θy.sub.i is the included angle between the acoustic axis and Z axis after the acoustic axis is projected on YOZ plane.

θx.sub.i=arcctan((C2.sub.X−C1.sub.X)/(b−a))  (1)

θy.sub.i=arcctan((C2.sub.Y−C1.sub.Y)/(b−a))  (2)

[0066] S6, selecting an adjustment threshold of 0.001 degrees according to the accuracy requirement of acoustic axis adjustment, judging whether the inclination angle θ.sub.i is less than the adjustment threshold, if so, aligning the acoustic axis, ending the adjustment, otherwise, proceeding to step S7;

[0067] S7, referring to the iterative algorithm given in the above specific implementation, calculating the inclination angle θ.sub.i=[θx.sub.i, θy.sub.i] of the acoustic axis and the coordinate PC.sub.i=[PC_X.sub.i, PC_Y.sub.i];

[0068] S8, keeping PC.sub.i of the X axis and Y axis unchanged, moving the Z axis to the focusing plane Z.sub.focus, manually adjusting two corner adjustment knobs of a probe clamping device until the amplitude of a hydrophone measurement signal at the current coordinate point is the maximum, and then proceeding to step S3.

[0069] The coordinates of θ.sub.i, PC.sub.i and C1, C2 under different numbers of iterations are shown in Table 1:

TABLE-US-00001 TABLE 1 θ (degrees) PC.sub.i (cm) C1 (cm) C2 (cm) θx.sub.i θy.sub.i PC_X.sub.i PC_Y.sub.i C1.sub.X C1.sub.Y C2.sub.X C2.sub.Y i = 1 4.57 6.91 −8.18 −7.48 −9.02 −8.75 −8.38 −7.78 i = 2 1.94 2.96 −8.96 −8.66 −9.32 −9.20 −9.05 −8.79 i = 3 −0.015 −0.042 −9.54 −9.55 −9.54 −9.54 −9.54 −9.54 i = 4 0.000035 0.000162 −9.53 −9.53 −9.53 −9.53 −9.53 −9.53

[0070] As can be seen from Table 1, after three iterations, the inclination angle θ.sub.i of the acoustic axis is smaller than the current adjustment threshold, 0.001 degrees, that is, the acoustic axis has been aligned.

[0071] In this embodiment, according to the measured data in the actual acoustic axis alignment process, the acoustic axis deviation angle projection on XOZ plane and YOZ plane and the results of a single adjustment amount are recorded, and FIG. 4 to FIG. 7 are plotted. FIG. 4 is a graph showing the change of the current deviation angle of a manual acoustic axis aligning method in XOZ plane with the number of iterations according to the present disclosure. FIG. 5 is a graph showing the change of a single adjustment amount of a manual acoustic axis aligning method in XOZ plane with the number of iterations according to the present disclosure. FIG. 6 is a graph showing the change of the cumin deviation angle of a manual acoustic axis aligning method in YOZ plane with the number of iterations according to the present disclosure. FIG. 7 is a graph showing the change of a single adjustment amount of a manual acoustic axis aligning method in YOZ plane with the number of iterations according to the present disclosure. It can be seen from FIG. 4 to FIG. 7 that the purpose that the current deviation angle and the single adjustment amount can be close to zero after three iterations in both planes can be achieved.

[0072] The above contents are only specific embodiments of the present disclosure to enable those skilled in the art to understand or realize the present disclosure. Many modifications to the above embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure.

[0073] It should be understood that the present disclosure is not limited to what has been described above, and various modifications and changes can be made without departing from the scope. The scope of the present disclosure is limited only by the appended claims.