A three-degree-of-freedom piezoelectric actuator and its working method

Abstract

The present invention discloses a three-degree-of-freedom piezoelectric actuator and its working method. The piezoelectric actuator includes a piezoelectric vibrator, a spherical rotor, a clamping frame, and first to fourth connecting rods; the piezoelectric vibrator includes a stator and first to eighth piezoelectric ceramic sheets. By applying excitation signals with a specific combination to the first to eighth piezoelectric ceramic sheets, two vibration modes out of one radial bending vibration mode and two orthogonal axial bending vibration modes of the stator are excited, so as to couple and form a micro-amplitude elliptical motion on the driving surface of the stator, and the spherical rotor is driven to obtain rotational motion in three degrees-of-freedom directions by using the frictional force. The present invention can achieve rotational motion in three degrees of freedom, has the advantages of simple structure, power-off self-locking, and easy miniaturization, and is applicable to fields such as space pointing mechanisms, optical target tracking, and robot joint technologies.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric actuators, and particularly relates to a three-degree-of-freedom piezoelectric actuator and its working method. Background Art

[0002] With the rapid development of precision drive technology, higher requirements and limitations are imposed on the performance of actuators in drive systems, demanding that they can achieve multi-degree-of-freedom motion, rapid response, no electromagnetic interference, miniaturization, etc. Conventional multi-degree-of-freedom actuators mainly achieve three-degree-of-freedom motion, multi-degree-of-freedom spherical electromagnetic motors, and multi-degree-of-freedom spatial parallel mechanisms by using the form of multiple single-degree-of-freedom electromagnetic motors connected in series. These structures all have complex transmission mechanisms, often resulting in large volume and complex structure. A multi-degree-of-freedom piezoelectric actuator is based on the inverse piezoelectric effect of piezoelectric materials to convert electrical energy into mechanical energy, exciting the stator to generate corresponding resonance modes, and realizing the multi-degree-of-freedom motion of the rotor under the drive of frictional force. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a three-degree-of-freedom piezoelectric actuator and its working method for the defects involved in the background art.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] A three-degree-of-freedom piezoelectric actuator includes a piezoelectric vibrator, a spherical rotor, a clamping frame, and first to fourth connecting rods;

[0006] The piezoelectric vibrator includes a stator and first to eighth piezoelectric ceramic sheets;

[0007] The stator is a hollow spherical frustum with open ends at both ends, and is symmetric about the neutral plane between the two bottom surfaces;

[0008] The first to eighth piezoelectric ceramic sheets have the same structure, are all block-shaped spherical shells, and each includes an outer wall, an inner wall, and first to fourth side walls connected end to end in sequence. Among them, the diameter of the inner wall is equal to the diameter of the outer spherical surface of the stator;

[0009] The first, third, fifth, and seventh piezoelectric ceramic sheets are circumferentially and uniformly arranged on the outer spherical surface of the stator, the second, fourth, sixth, and eighth piezoelectric ceramic sheets are circumferentially and uniformly arranged on the outer spherical surface of the stator, and the first and second piezoelectric ceramic sheets, the third and fourth piezoelectric ceramic sheets, the fifth and sixth piezoelectric ceramic sheets, and the seventh and eighth piezoelectric ceramic sheets are all symmetric about the neutral plane between the two bottom surfaces of the stator; the first and third side walls of the first to eighth piezoelectric ceramic sheets are all parallel to the bottom surface of the stator, and the second and fourth side walls of the first to eighth piezoelectric ceramic sheets are all coplanar with the axis of the stator; the first to eighth piezoelectric ceramic sheets are all polarized in the thickness direction and the polarization directions are all inward;

[0010] The spherical rotor is a sphere or a spherical frustum symmetric about the neutral plane between two bottom surfaces, is arranged inside the stator, and is in spherical contact with the stator.

[0011] The clamping frame encloses the stator; the first to fourth connecting rods are circumferentially and uniformly arranged outside the stator, one ends of the first to fourth connecting rods are respectively fixedly connected to the four intersection points of the four pitch circles and pitch diameters in the working mode of the stator, and the other ends are fixedly connected to the clamping frame.

[0012] As a further optimization scheme of the three-degree-of-freedom piezoelectric actuator of the present invention, the clamping frame is a square frame, and threaded through holes for fixedly connecting with the outside are provided at the four midpoints of the four sides thereof.

[0013] As a further optimization scheme of the three-degree-of-freedom piezoelectric actuator of the present invention, one ends of the first to fourth connecting rods close to the stator are concave spherical surfaces matching the stator.

[0014] As a further optimization scheme of the three-degree-of-freedom piezoelectric actuator of the present invention, the spherical rotor is a spherical frustum symmetric about the neutral plane between two bottom surfaces, and a circular through hole for arranging an output shaft is provided along the axis thereof.

[0015] The present invention also discloses a working method of the three-degree-of-freedom piezoelectric actuator, including the following steps:

[0016] Let the center of the sphere of the stator be the origin of the Cartesian coordinate system, the angular bisecting plane of the plane where the second and fourth side walls of the first piezoelectric ceramic sheet are located be plane A, the angular bisecting plane of the plane where the second and fourth side walls of the third piezoelectric ceramic sheet are located be plane B, and the neutral plane between the two bottom surfaces of the stator be C. The positive direction of the X axis is outward along the intersection line of plane A and plane C from the coordinate origin, the positive direction of the Y axis is outward along the intersection line of plane B and plane C from the coordinate origin, and the positive direction of the Z axis is the direction from the coordinate origin along the axis of the stator towards the bottom surface of the stator close to the first piezoelectric ceramic sheet.

[0017] If it is necessary to drive the spherical rotor to rotate around the X axis:

[0018] Apply a first excitation signal to the first, second, fifth, and sixth piezoelectric ceramic wafers, a second excitation signal to the third and eighth piezoelectric ceramic wafers, and a third excitation signal to the fourth and seventh piezoelectric ceramic wafers. The first to third excitation signals are all AC harmonic signals with the same frequency and amplitude. The first excitation signal leads the second excitation signal by π / 2 in time phase difference, and the second excitation signal has a phase opposite to that of the third excitation signal, so that the piezoelectric vibrator simultaneously excites the radial bending vibration mode and the axial bending vibration mode in the Y-axis direction; through the coupling of the radial bending vibration mode and the axial bending vibration mode in the Y-axis direction, a small-amplitude elliptical motion perpendicular to the X-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the X-axis through the frictional effect;

[0019] If reverse rotation around the X-axis is required, just reverse the phase of the first excitation signal;

[0020] If it is necessary to drive the spherical rotor to rotate around the Y-axis:

[0021] Apply a first excitation signal to the third, fourth, seventh, and eighth piezoelectric ceramic wafers, a second excitation signal to the first and sixth piezoelectric ceramic wafers, and a third excitation signal to the second and fifth piezoelectric ceramic wafers. The first to third excitation signals are all AC harmonic signals with the same frequency and amplitude. The first excitation signal leads the second excitation signal by π / 2 in time phase difference, and the second excitation signal has a phase opposite to that of the third excitation signal, so that the piezoelectric vibrator simultaneously excites the radial bending vibration mode and the axial bending vibration mode in the X-axis direction; through the coupling of the radial bending vibration mode and the axial bending vibration mode in the X-axis direction, a small-amplitude elliptical motion perpendicular to the Y-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the Y-axis through the frictional effect;

[0022] If reverse rotation around the Y-axis is required, just reverse the phase of the first excitation signal;

[0023] If it is necessary to drive the spherical rotor to rotate around the Z-axis:

[0024] Apply a fourth excitation signal to the first and sixth piezoelectric ceramic wafers, a fifth excitation signal to the second and fifth piezoelectric ceramic wafers, a sixth excitation signal to the third and eighth piezoelectric ceramic wafers, and a seventh excitation signal to the fourth and seventh piezoelectric ceramic wafers. The first to seventh excitation signals are all AC harmonic signals with the same frequency and amplitude. The fourth excitation signal leads the sixth excitation signal by π / 2 in time phase difference, the fourth excitation signal has a phase opposite to that of the sixth excitation signal, and the fifth excitation signal has a phase opposite to that of the seventh excitation signal, so that the piezoelectric vibrator simultaneously has two orthogonal axial bending vibration modes; through the coupling of the two orthogonal axial bending vibration modes, a small-amplitude elliptical motion perpendicular to the Z-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the Z-axis through the frictional effect;

[0025] If reverse rotation about the Z-axis is required, the fourth excitation signal can be changed to lag the sixth excitation signal by π / 2 in terms of time phase difference.

[0026] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0027] 1. By using a patch structure to paste the piezoelectric ceramic sheet on the outer spherical surface of the stator, the structure of the piezoelectric vibrator can be simplified, and the size of the actuator can be effectively reduced;

[0028] 2. By adopting spherical contact between the stator and the spherical rotor, it is beneficial to increase the driving surface and improve the efficiency of the actuator. Description of the Drawings

[0029] Figure 1 is a schematic structural diagram of the present invention;

[0030] Figure 2 is a schematic structural diagram of the piezoelectric vibrator in the present invention;

[0031] Figure 3 is a schematic diagram of the polarization directions of the first to eighth piezoelectric ceramic sheets in the present invention;

[0032] Figure 4 is a schematic structural diagram of the spherical rotor in the present invention;

[0033] Figure 5 is a schematic structural diagram of the clamping frame and the first to fourth connecting rods cooperating with each other in the present invention;

[0034] Figure 6 is a schematic diagram comparing the radial bending vibration modes of the piezoelectric vibrator with a 180-degree phase difference in the XOY plane in the present invention

[0035] Figure 7 is a schematic diagram comparing the axial bending vibration modes in the Y-axis direction of the piezoelectric vibrator with a 180-degree phase difference in the XOZ plane in the present invention;

[0036] Figure 8 is a schematic diagram comparing the axial bending vibration modes in the X-axis direction of the piezoelectric vibrator with a 180-degree phase difference in the XOZ plane in the present invention;

[0037] Figure 9 is a schematic diagram of the working state of the piezoelectric vibrator when the present invention rotates about the X-axis;

[0038] Figure 10 is a schematic diagram of the working state of the piezoelectric vibrator when the present invention rotates about the Y-axis;

[0039] Figure 11 is a schematic diagram of the working state of the piezoelectric vibrator when the present invention rotates about the X-axis.

[0040] In the figure, 1 - piezoelectric vibrator, 2 - spherical rotor, 3 - clamping frame, 4 - stator, 5 - fifth piezoelectric ceramic sheet, 6 - circular through - hole on the spherical rotor, 7 - rectangular frame, 8 - first connecting rod, 9 - threaded through - hole on the clamping frame. Embodiment

[0041] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0042] The present invention can be implemented in many different forms and should not be considered limited to the embodiments described herein. On the contrary, these embodiments are provided so that this disclosure is thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the drawings, components are enlarged for clarity.

[0043] It should be understood that although the terms first, second, third, etc. may be used herein to describe various elements, components, and / or parts, these elements, components, and / or parts are not limited by these terms. These terms are only used to distinguish one element, component, and / or part from another. Thus, the first element, component, and / or part discussed below may become the second element, component, or part without departing from the teachings of the present invention.

[0044] As Figure 1 shown, the present invention discloses a three - degree - of - freedom piezoelectric actuator, comprising a piezoelectric vibrator, a spherical rotor, a clamping frame, and first to fourth connecting rods;

[0045] As Figure 2 shown, the piezoelectric vibrator includes a stator and first to eighth piezoelectric ceramic sheets;

[0046] The stator is a hollow spherical frustum with open ends at both ends and is symmetric about the neutral plane between the two bottom surfaces;

[0047] The first to eighth piezoelectric ceramic sheets have the same structure, are all block - shaped spherical shells, and each includes an outer wall, an inner wall, and first to fourth side walls connected end to end in sequence. Among them, the diameter of the inner wall is equal to the diameter of the outer spherical surface of the stator;

[0048] The first, third, fifth, and seventh piezoelectric ceramic sheets are circumferentially and uniformly arranged on the outer spherical surface of the stator, the second, fourth, sixth, and eighth piezoelectric ceramic sheets are circumferentially and uniformly arranged on the outer spherical surface of the stator, and the first and second piezoelectric ceramic sheets, the third and fourth piezoelectric ceramic sheets, the fifth and sixth piezoelectric ceramic sheets, and the seventh and eighth piezoelectric ceramic sheets are all symmetric about the neutral plane between the two bottom surfaces of the stator; the first and third side walls of the first to eighth piezoelectric ceramic sheets are all parallel to the bottom surface of the stator, and the second and fourth side walls of the first to eighth piezoelectric ceramic sheets are all coplanar with the axis of the stator; the first to eighth piezoelectric ceramic sheets are all polarized in the thickness direction and the polarization directions are all inward, as Figure 3 shown;

[0049] The spherical rotor is a sphere or a spherical frustum symmetric about the neutral plane between two bottom surfaces, is arranged inside the stator, and is in spherical contact with the stator.

[0050] The clamping frame contains the stator; the first to fourth connecting rods are circumferentially and uniformly arranged outside the stator, one ends of the first to fourth connecting rods are respectively fixedly connected to the four intersection points of the four pitch circles and pitch diameters in the working mode of the stator, and the other ends are fixedly connected to the clamping frame.

[0051] As Figure 4 shown, when the spherical rotor is a spherical frustum symmetric about the neutral plane between two bottom surfaces, it is provided with a circular through hole for arranging an output shaft along the axis.

[0052] As Figure 5 shown, when the clamping frame is a square frame, threaded through holes for fixedly connecting to the outside are provided at the four midpoints of the four sides thereof.

[0053] One ends of the first to fourth connecting rods close to the stator are all concave spherical surfaces that cooperate with the stator.

[0054] The first to fourth connecting rods are fixedly connected to the outer spherical surface of the stator, and the connection positions are at the intersection points of the pitch circle and pitch diameter in the working mode of the stator, that is, the four points on the outer spherical surface of the stator passed through by two straight lines forming an angle of 45 degrees and -45 degrees with the X-axis in the XOY plane of the stator.

[0055] The greater the height of the spherical rotor, the greater the range of the rotatable angle, and the range of the rotatable angle is the largest when a sphere is adopted.

[0056] The present invention also discloses a working method of the three-degree-of-freedom piezoelectric actuator, including the following steps:

[0057] Let the center of the sphere of the stator be the origin of the Cartesian coordinate system, the angular bisecting plane of the plane where the second and fourth side walls of the first piezoelectric ceramic sheet are located be plane A, the angular bisecting plane of the plane where the second and fourth side walls of the third piezoelectric ceramic sheet are located be plane B, the neutral plane between the two bottom surfaces of the stator be C, the positive direction of the X-axis be outward along the intersection line of plane A and plane C from the coordinate origin, the positive direction of the Y-axis be outward along the intersection line of plane B and plane C from the coordinate origin, and the positive direction of the Z-axis be along the axis of the stator and point to the bottom surface of the stator close to the first piezoelectric ceramic sheet from the coordinate origin;

[0058] If it is necessary to drive the spherical rotor to rotate around the X-axis:

[0059] Apply a first excitation signal to the first, second, fifth, and sixth piezoelectric ceramic sheets, a second excitation signal to the third and eighth piezoelectric ceramic sheets, and a third excitation signal to the fourth and seventh piezoelectric ceramic sheets. The first to third excitation signals are all AC harmonic signals with the same frequency and amplitude. The first excitation signal leads the second excitation signal by π / 2 in time phase difference, and the second excitation signal has a phase opposite to that of the third excitation signal, so that the piezoelectric vibrator simultaneously excites a radial bending vibration mode and an axial bending vibration mode in the Y-axis direction, as Figure 6 and Figure 7 shown; through the coupling of the radial bending vibration mode and the axial bending vibration mode in the Y-axis direction, a micro-amplitude elliptical motion perpendicular to the X-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the X-axis through the frictional action, as Figure 9 shown;

[0060] If reverse rotation around the X-axis is required, just reverse the phase of the first excitation signal;

[0061] If it is necessary to drive the spherical rotor to rotate around the Y-axis:

[0062] Apply a first excitation signal to the third, fourth, seventh, and eighth piezoelectric ceramic sheets, a second excitation signal to the first and sixth piezoelectric ceramic sheets, and a third excitation signal to the second and fifth piezoelectric ceramic sheets. The first to third excitation signals are all AC harmonic signals with the same frequency and amplitude. The first excitation signal leads the second excitation signal by π / 2 in time phase difference, and the second excitation signal has a phase opposite to that of the third excitation signal, so that the piezoelectric vibrator simultaneously excites a radial bending vibration mode and an axial bending vibration mode in the X-axis direction, as Figure 6 and Figure 8 shown; through the coupling of the radial bending vibration mode and the axial bending vibration mode in the X-axis direction, a micro-amplitude elliptical motion perpendicular to the Y-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the Y-axis through the frictional action, as Figure 10 shown;

[0063] If reverse rotation around the Y-axis is required, just reverse the phase of the first excitation signal;

[0064] If it is necessary to drive the spherical rotor to rotate around the Z-axis:

[0065] Apply a fourth excitation signal to the first and sixth piezoelectric ceramic sheets, a fifth excitation signal to the second and fifth piezoelectric ceramic sheets, a sixth excitation signal to the third and eighth piezoelectric ceramic sheets, and a seventh excitation signal to the fourth and seventh piezoelectric ceramic sheets. The first to seventh excitation signals are all AC harmonic signals with the same frequency and amplitude. The fourth excitation signal leads the sixth excitation signal by π / 2 in time phase difference, the fourth excitation signal has a phase opposite to that of the sixth excitation signal, and the fifth excitation signal has a phase opposite to that of the seventh excitation signal, so that the piezoelectric vibrator simultaneously has two orthogonal axial bending vibration modes, asFigure 7 and Figure 8 as shown; through the coupling of two orthogonal axial bending vibration modes, a small-amplitude elliptical motion perpendicular to the Z-axis is formed on the driving surface of the piezoelectric oscillator, and the spherical rotor is driven to rotate around the Z-axis through frictional action, as Figure 11 shown;

[0066] If reverse rotation around the Z-axis is required, the fourth excitation signal can be changed to lag behind the sixth excitation signal by π / 2 in time phase difference.

[0067] While retaining the advantages of simple structure, flexibility, rapid response, and no electromagnetic interference of the piezoelectric actuator, the multi-degree-of-freedom piezoelectric actuator can also achieve multi-degree-of-freedom motion. The use of a patch-type spherical shell stator can simplify the structure of the piezoelectric oscillator and effectively reduce the size of the actuator. In addition, the use of a spherical shell stator in contact with the spherical surface of the spherical rotor for driving is beneficial to increasing the driving surface and improving the efficiency of the actuator.

[0068] Those skilled in the art of this technology can understand that, unless otherwise defined, all terms used herein (including technical terms and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the field to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless defined as such here.

[0069] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A three-degree-of-freedom piezoelectric actuator, characterized in that, It includes a piezoelectric vibrator, a spherical rotor, a clamping frame, and first to fourth connecting rods; The piezoelectric vibrator includes a stator and first to eighth piezoelectric ceramic sheets; The stator is a hollow spherical frustum with open ends at both ends, and it is symmetric about the neutral plane between the two bottom surfaces; The first to eighth piezoelectric ceramic sheets have the same structure, are all block-shaped spherical shells, and all include an outer wall, an inner wall, and first to fourth side walls connected end to end in sequence. Among them, the diameter of the inner wall is equal to the diameter of the outer spherical surface of the stator; The first, third, fifth, and seventh piezoelectric ceramic sheets are circumferentially and evenly arranged on the outer spherical surface of the stator, the second, fourth, sixth, and eighth piezoelectric ceramic sheets are circumferentially and evenly arranged on the outer spherical surface of the stator, and the first and second piezoelectric ceramic sheets, the third and fourth piezoelectric ceramic sheets, the fifth and sixth piezoelectric ceramic sheets, and the seventh and eighth piezoelectric ceramic sheets are all symmetric about the neutral plane between the two bottom surfaces of the stator; the first and third side walls of the first to eighth piezoelectric ceramic sheets are all parallel to the bottom surface of the stator, and the second and fourth side walls of the first to eighth piezoelectric ceramic sheets are all coplanar with the axis of the stator; the first to eighth piezoelectric ceramic sheets are all polarized along the thickness direction and the polarization directions are all inward; The spherical rotor is a sphere or a spherical frustum symmetric about the neutral plane between the two bottom surfaces, is arranged inside the stator, and is in contact with the spherical surface of the stator; The clamping frame includes the stator therein; the first to fourth connecting rods are circumferentially and evenly arranged outside the stator, and one ends of the first to fourth connecting rods are respectively fixedly connected to the four intersection points of the four pitch circles and pitch diameters in the working mode of the stator in a one-to-one correspondence, and the other ends are fixedly connected to the clamping frame.

2. The three-degree-of-freedom piezoelectric actuator according to claim 1, wherein The clamping frame is a square frame, and threaded through holes for connecting to the outside are provided at the four midpoints of the four sides thereof.

3. The three-degree-of-freedom piezoelectric actuator according to claim 1, characterized in that, One ends of the first to fourth connecting rods close to the stator are concave spherical surfaces that match the stator.

4. The three-degree-of-freedom piezoelectric actuator according to claim 1, characterized in that The spherical rotor is a spherical frustum symmetric about the neutral plane between the two bottom surfaces, and a circular through hole for arranging an output shaft is provided along its axis.

5. The working method of the three-degree-of-freedom piezoelectric actuator according to claim 1, characterized in that, It includes the following steps: Let the center of the sphere of the stator be the origin of the Cartesian coordinate system, the angular bisecting plane of the plane where the second and fourth side walls of the first piezoelectric ceramic sheet are located be plane A, the angular bisecting plane of the plane where the second and fourth side walls of the third piezoelectric ceramic sheet are located be plane B, and the neutral plane between the two bottom surfaces of the stator be C. The positive direction of the X axis is outward along the intersection line of plane A and plane C from the coordinate origin, the positive direction of the Y axis is outward along the intersection line of plane B and plane C from the coordinate origin, and the positive direction of the Z axis is along the axis of the stator and points to the bottom surface of the stator close to the first piezoelectric ceramic sheet from the coordinate origin; If it is necessary to drive the spherical rotor to rotate around the X axis: Apply a first excitation signal to the first, second, fifth, and sixth piezoelectric ceramic wafers, a second excitation signal to the third and eighth piezoelectric ceramic wafers, and a third excitation signal to the fourth and seventh piezoelectric ceramic wafers. The first to third excitation signals are all AC harmonic signals with the same frequency and amplitude. The first excitation signal leads the second excitation signal by π / 2 in time phase difference, and the second excitation signal has a phase opposite to that of the third excitation signal, so that the piezoelectric vibrator simultaneously excites the radial bending vibration mode and the axial bending vibration mode in the Y-axis direction; through the coupling of the radial bending vibration mode and the axial bending vibration mode in the Y-axis direction, a small-amplitude elliptical motion perpendicular to the X-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the X-axis through the friction effect; If reverse rotation around the X-axis is required, just invert the phase of the first excitation signal; If it is necessary to drive the spherical rotor to rotate around the Y-axis: Apply a first excitation signal to the third, fourth, seventh, and eighth piezoelectric ceramic wafers, a second excitation signal to the first and sixth piezoelectric ceramic wafers, and a third excitation signal to the second and fifth piezoelectric ceramic wafers. The first to third excitation signals are all AC harmonic signals with the same frequency and amplitude. The first excitation signal leads the second excitation signal by π / 2 in time phase difference, and the second excitation signal has a phase opposite to that of the third excitation signal, so that the piezoelectric vibrator simultaneously excites the radial bending vibration mode and the axial bending vibration mode in the X-axis direction; through the coupling of the radial bending vibration mode and the axial bending vibration mode in the X-axis direction, a small-amplitude elliptical motion perpendicular to the Y-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the Y-axis through the friction effect; If reverse rotation around the Y-axis is required, just invert the phase of the first excitation signal; If it is necessary to drive the spherical rotor to rotate around the Z-axis: Apply a fourth excitation signal to the first and sixth piezoelectric ceramic wafers, a fifth excitation signal to the second and fifth piezoelectric ceramic wafers, a sixth excitation signal to the third and eighth piezoelectric ceramic wafers, and a seventh excitation signal to the fourth and seventh piezoelectric ceramic wafers. The first to seventh excitation signals are all AC harmonic signals with the same frequency and amplitude. The fourth excitation signal leads the sixth excitation signal by π / 2 in time phase difference, the fourth excitation signal has a phase opposite to that of the sixth excitation signal, and the fifth excitation signal has a phase opposite to that of the seventh excitation signal, so that the piezoelectric vibrator simultaneously excites two orthogonal axial bending vibration modes; through the coupling of the two orthogonal axial bending vibration modes, a small-amplitude elliptical motion perpendicular to the Z-axis is formed on the driving surface of the piezoelectric vibrator, and the spherical rotor is driven to rotate around the Z-axis through the friction effect; If reverse rotation around the Z-axis is required, just change the fourth excitation signal to lag the sixth excitation signal by π / 2 in time phase difference.

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