A rotary piezoelectric ultrasonic motor and a driving method thereof

Abstract

The present invention discloses a rotary piezoelectric ultrasonic motor and a driving method, wherein the motor comprises a stator, a rotor, a bearing and a pre-stress device. The stator is composed of a base and an even number of piezoelectric vibrators of not less than 6 uniformly distributed along the circumferential direction, wherein a protrusion is arranged on the upper end of each piezoelectric vibrator as a friction head and in contact with the rotor. The stator has two vibration modes with approximately equal resonance frequencies: two adjacent piezoelectric vibrators of one mode perform bending vibrations in opposite directions along the circumferential tangent direction, and two adjacent piezoelectric vibrators of the other mode perform longitudinal stretching vibrations in opposite directions. The piezoelectric vibrator is provided with three electrodes, one electrode is grounded, and the other two electrodes are applied with an AC voltage Vsin (2πf d t) and #imgabs0# friction head produce a slight elliptical motion. By changing V, f d , and #imgabs1# are used to adjust the amplitude of the elliptical motion, thereby changing the driving force and speed of the motor.

Description

Technical Field

[0001] The present invention belongs to the technical field of precision driving elements, and in particular relates to a rotary piezoelectric ultrasonic motor and a driving method thereof. Background Art

[0002] Compared with traditional motors, ultrasonic motors have the following characteristics: simple and compact structure, large torque / volume ratio, low speed and high torque, no need for gear reduction mechanism, direct drive, fast response (millisecond level), power-off self-locking, high resolution, high precision under closed-loop control, no magnetic field, no interference from external magnetic field, and diversified shapes (round, square, hollow, rod-shaped), etc. Due to its unique performance, ultrasonic motors are superior to electromagnetic motors in many occasions and have broad application prospects, especially in application fields that require fast response and high-precision position control (such as precision drive of optical elements in medical imaging systems). Ultrasonic motors have shown obvious superiority in terms of motion range, driving force, driving accuracy, response speed and power consumption. In the field of industrial control, ultrasonic motors are also gradually gaining more applications. The rotary piezoelectric ultrasonic motor disclosed in US Pat. No. 4,562,374 utilizes the bending traveling wave of the ultrasonic frequency band excited in the annular elastic body to drive the rotor in contact therewith to produce a rotational motion. All the surface particles of the elastic body stator make elliptical motions of equal amplitude. The area of ​​its friction drive interface is large, so it can generate a large driving torque, and has been applied to drive the camera lens to realize the automatic focusing function. The bending traveling wave in this annular stator is generated by the superposition of two equal-amplitude bending standing waves that differ by 1 / 4 wavelength in space and 90° in phase. However, the shape of the elliptical motion trajectory of the particles on the friction drive interface of the stator of the traveling wave type ultrasonic motor cannot be adjusted at will (the ratio of the tangential amplitude to the normal amplitude is determined by the geometric size of the stator), and the tangential amplitude and the normal amplitude can only increase or decrease in the same proportion, resulting in the instability of the motor when running at a low speed, and it is difficult to control it with high precision.

[0003] In order to meet the needs of scientific instruments, biomedicine, aerospace and other products for high-precision actuators, it is necessary to invent a new rotary piezoelectric ultrasonic motor and driving method. Summary of the invention

[0004] The purpose of the present invention is to provide a new rotary piezoelectric ultrasonic motor and its driving method in view of various drawbacks of the rotary piezoelectric ultrasonic motor in actual use; the tangential amplitude and normal amplitude of the friction head can be independently adjusted to improve the control accuracy.

[0005] The rotary piezoelectric ultrasonic motor of the present invention adopts the following technical solutions:

[0006] A rotary piezoelectric ultrasonic motor, comprising a stator, a rotor, and a bearing. The stator comprises a base, and at least six rectangular-section columnar piezoelectric vibrators mounted on the upper surface of the base and evenly distributed along the circumferential direction. A protrusion is provided on the upper end of each piezoelectric vibrator as a friction head. An axial through hole is provided at the central position of the stator, and a bearing is installed in the through hole.

[0007] The rotor comprises a rotating disk and a rotating shaft extending downward from the rotating disk, the rotating shaft is sleeved in a bearing, and the lower surface of the rotating disk contacts all friction heads on the stator;

[0008] The stator has two vibration modes with approximately equal resonant frequencies, namely the B-mode mode and the L-mode mode;

[0009] When in the B-mode, two adjacent piezoelectric vibrators perform bending vibrations in opposite directions; the bending direction is tangential to the circumference;

[0010] When in the L-mode, two adjacent piezoelectric vibrators perform longitudinal expansion and contraction vibrations in opposite directions.

[0011] Furthermore, each of the piezoelectric vibrators has the same structure, and the piezoelectric vibrator includes a metal elastomer and two piezoelectric sheets respectively covering the inner and outer sides of the metal elastomer; the side of the piezoelectric sheet bonded to the metal elastomer is a fully covered inner surface electrode, and the side of the piezoelectric sheet facing away from the metal elastomer is two metal electrode areas separated in the middle, and the two metal electrode areas serve as the second electrode and the third electrode, and the parts of the piezoelectric sheet covered by the second electrode and the third electrode are polarized in the same direction along the thickness direction; the polarization directions of the two piezoelectric sheets of the same piezoelectric vibrator are opposite; the inner surface electrode is connected to the base as a ground electrode; when the second electrode and the third electrode are applied with an AC voltage of the same phase close to the resonance frequency, the stator L-mode mode is excited, and when the second electrode and the third electrode are applied with an AC voltage of opposite phase close to the resonance frequency, the stator B-mode mode is excited.

[0012] Furthermore, each of the piezoelectric vibrators has the same structure, and the piezoelectric vibrator includes a laminated piezoelectric ceramic column formed by co-firing piezoelectric ceramics and metal electrodes, and a friction head located at the top of the laminated piezoelectric ceramic column; the laminated piezoelectric ceramic column includes a plurality of sheet piezoelectric ceramics arranged side by side, a first electrode or an electrode group is sandwiched between two adjacent sheet piezoelectric ceramics, the electrode group includes a second electrode and a third electrode separated in the middle, and a plurality of first electrodes and a plurality of electrode groups are alternately inserted between a plurality of sheet piezoelectric ceramics, wherein the first electrode is grounded, and when the second electrode and the third electrode are applied with an AC voltage of the same phase close to the resonance frequency, a stator L-mode mode is excited, and when the second electrode and the third electrode are applied with an AC voltage of opposite phase close to the resonance frequency, a stator B-mode mode is excited.

[0013] Furthermore, the number of the columnar piezoelectric vibrators is an even number 2n, where n≥3.

[0014] Beneficial effects: The tangential amplitude and normal amplitude of the stator friction drive head of the rotary piezoelectric ultrasonic motor provided by the present invention can be adjusted independently; when the motor needs to run at a low speed, the vibration of the stator should be controlled to reduce the tangential amplitude of the friction head, while maintaining the amplitude of the normal vibration, that is, a larger driving force can be maintained while reducing the speed; the low-speed operation stability of the ultrasonic motor can be improved, and the accuracy of motion control can be improved.

[0015] The driving method of the rotary piezoelectric ultrasonic motor can adopt the following technical solutions:

[0016] The ground electrode is grounded, and the second electrode and the third electrode are respectively applied with an AC voltage V1=Vsin(2πf d t) and The friction head at the upper end of the piezoelectric vibrator produces a slight elliptical motion, and the rotor rotates due to the friction force; where V is the amplitude of the voltage, f d is the frequency, t is the time, is the phase difference.

[0017] By changing the amplitude V and frequency f of the applied voltage d , and phase difference To adjust the amplitude of the elliptical motion of the friction head, thereby changing the driving force and speed of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall structure of a rotary piezoelectric ultrasonic motor according to an embodiment of the present invention.

[0019] Figure 2 for Figure 1 Exploded view of a rotary piezoelectric ultrasonic motor.

[0020] Figure 3 It is a schematic diagram of the overall structure of the motor stator.

[0021] Figure 4 for Figure 3 Exploded view of the motor stator.

[0022] Figure 5 It is a side view simulation schematic diagram of the natural vibration mode B-mode of the motor stator.

[0023] Figure 6 It is a top view simulation schematic diagram of the natural vibration mode B-mode of the motor stator.

[0024] Figure 7 It is a side view simulation schematic diagram of the natural vibration mode L-mode of the motor stator.

[0025] Figure 8 It is a top view simulation schematic diagram of the natural vibration mode L-mode of the motor stator.

[0026] Fig. 9 The figure is a schematic diagram of the structure of the piezoelectric vibrator.

[0027] Fig.10 Schematic diagram of the surface electrodes of the piezoelectric film.

[0028] Fig.11 It is a schematic diagram of the driving method of the rotary piezoelectric ultrasonic motor of the present invention.

[0029] Fig.12 A schematic diagram of the structure of another piezoelectric vibrator.

[0030] Fig.13 for Fig.12 Schematic diagram of the internal interlayer electrodes and external side electrodes of the medium-stack piezoelectric ceramic column.

[0031] Fig.14 for Fig.12 Schematic diagram of the outer side electrodes and grounding of the medium voltage electric vibrator.

[0032] Fig.15 Schematic diagram of a driving method for an ultrasonic motor using a laminated piezoelectric ceramic column.

[0033] Fig.16 Schematic diagram of the relationship between the motor stator amplitude and the driving voltage frequency.

[0034] Fig.17 This diagram shows the relationship between the voltage applied to a piezoelectric element and the vibration mode using vectors.

[0035] Fig.18 Schematic diagram of the relationship between the motor stator amplitude and the driving voltage |V1+V2| and |V1-V2| (the driving frequency remains unchanged).

[0036] Fig.19 It is a schematic diagram of the projection of the motion trajectory of the end of the motor stator friction head in the zθ plane. DETAILED DESCRIPTION

[0037] In order to make the technical method and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0038] like Figure 1 and Figure 2 As shown, the present invention provides a rotary piezoelectric ultrasonic motor 1, comprising a stator 2, a rotor 3, two bearings 4, and a pre-pressure device.

[0039] like Figure 3 and Figure 4 As shown, the structure of the stator 2 includes a base 21, and six rectangular-section columnar piezoelectric vibrators 22-1, 22-2, 22-3, 22-4, 22-5, and 22-6 installed on the upper surface of the base and evenly distributed in the circumferential direction. A protrusion is set on the upper end of each piezoelectric vibrator as a friction head 224 and contacts with the rotor 3.

[0040] In this embodiment, 6 columnar piezoelectric vibrators are used. In other embodiments, the number of columnar piezoelectric vibrators can be 2n, n ≥ 3, that is, an even number of columnar piezoelectric vibrators greater than or equal to 6 can be used to implement the technical solution of the present invention. In this embodiment, the technical solution is described with the setting of 6 columnar piezoelectric vibrators as a preferred embodiment.

[0041] The stator 2 has an axial through hole, a bearing 4-1 is installed at its lower end, and a bearing 4-2 is installed at its upper end.

[0042] The rotor 3 includes a rotating disk 31 and a rotating shaft 32. The rotating shaft 32 is inserted into the two bearings 4, and the rotating disk 31 is in contact with the six friction heads 224 on the stator 2.

[0043] The elastic preload device is a spring 5 and a nut 6, the nut 6 is mounted on the shaft of the rotor 3, and the spring 5 which is sleeved on the rotor shaft and compressed is located between the bearing 4-1 and the nut 6. The force of the spring 5 keeps the rotor 3 in contact with the stator 2.

[0044] The size of the piezoelectric vibrator 22 is set so that its bending vibration mode and longitudinal extension vibration mode have overlapping resonant frequencies. Accordingly, the stator 2 has two vibration modes, one of which has a resonant frequency of f B The vibration shape of the mode (B-mode) (see Figure 5 and Figure 6 ) The first, third, and fifth piezoelectric vibrators 22-1, 22-3, and 22-5 and the second, fourth, and sixth piezoelectric vibrators 22-2, 22-4, and 22-6 perform bending vibrations in opposite directions (the bending direction is along the circumferential tangent direction, and the tangential component of the amplitude at the end of the friction head is as follows: Figure 6 Middle A θ As shown), the other resonant frequency is f L The vibration shape of the mode (L-mode) (see Figure 7 and Figure 8 ) The first, third, and fifth piezoelectric vibrators 22-1, 22-3, and 22-5 and the second, fourth, and sixth piezoelectric vibrators 22-2, 22-4, and 22-6 perform longitudinal expansion and contraction vibrations in opposite directions (the axial component of the amplitude at the end of the friction head is as follows: Figure 7 Middle A z As shown), the two resonant frequencies are approximately equal (fB ≈f L ).

[0045] Fig. 9 The structure of the piezoelectric vibrator 22 includes a metal elastic body 221 (made of a material with a high mechanical quality factor such as phosphor bronze) and two piezoelectric sheets 222 (made of piezoelectric ceramics or piezoelectric single crystal materials). The piezoelectric sheets 222 are bonded and assembled with the metal elastic body 221 .

[0046] Fig.10 Schematic diagram of the surface electrode (a thin layer of conductive metal) of the piezoelectric sheet 222. The side of the piezoelectric sheet 222 bonded to the metal elastomer 221 is a fully covered electrode 222a, and the other side is two separated metal electrode areas 222b. Both parts of the piezoelectric sheet are polarized in the same direction along the thickness direction. The polarization treatment of piezoelectric materials belongs to material pretreatment. It is to apply a high DC voltage to the metal electrode on the surface of the ferroelectric piezoelectric material and maintain it for a period of time, so that the electric dipoles are turned to a consistent arrangement. After the treatment, the piezoelectric material undergoes a permanent change.

[0047] Fig.11 The driving method of the rotary piezoelectric ultrasonic motor 1 of the embodiment of the present invention. The polarization direction of the piezoelectric sheet 222 is shown in the direction of the arrow in the figure. The polarization directions of the two piezoelectric sheets of the same piezoelectric vibrator 21 are opposite, and the polarization directions of the piezoelectric sheets of two adjacent piezoelectric vibrators 21 are opposite. The inner surface electrodes 222a (a total of 12) of all piezoelectric sheets 222 bonded to the metal elastomer 221 are connected to the stator base 21 (made of metal material), defined as the first electrode, and grounded during driving. The outer surface electrode area 222b (a total of 24) of the piezoelectric sheet 222 is divided into two groups according to the left and right directions, and is defined as the second electrode and the third electrode respectively. When the second and third electrodes are applied with an AC voltage close to the resonance frequency in the same phase, the stator L-mode can be excited, and when an AC voltage close to the resonance frequency in the opposite phase (phase difference of 180°) is applied, the stator B-mode can be excited. When the rotary piezoelectric ultrasonic motor 1 is driven to work, the first electrode is grounded, and the second and third electrodes are respectively applied with an AC voltage V1=Vsin(2πf d t) and The friction head at the upper end of the piezoelectric vibrator produces a slight elliptical motion, and the rotor rotates due to the friction force.

[0048] Fig.12Another embodiment of the present invention is shown: the piezoelectric vibrator 22 includes a laminated piezoelectric ceramic column 223 and a friction head 224, and the friction head 224 is bonded and assembled with the laminated piezoelectric ceramic column 223. The friction head 224 is made of a wear-resistant material (such as high-density Al2O3, ZrO2 ceramics, etc.). The laminated piezoelectric ceramic vibrator 22 is bonded and assembled with the metal base 21 to form the ultrasonic motor stator 2. The laminated piezoelectric ceramic vibrator 22 and the metal base 21 are bonded and assembled to form the ultrasonic motor stator 2. Fig. 9 The difference between the metal elastomer-piezoelectric film composite vibrator 22 in the shown embodiment is that the laminated piezoelectric ceramic column 223 is composed of many stacked piezoelectric ceramic sheets (such as Pb(Zr,Ti)O3 ceramics, tens to several microns thick), which can be prepared by low-temperature co-firing technology of ceramic / metal inner electrodes. It has the advantages of low driving voltage, large electro-induced strain, and the ability to operate in a low-frequency non-resonant state. However, the bonding strength between the co-fired ceramic layers is low and it is easily damaged under large-amplitude vibration.

[0049] Fig.13 and Fig.14 They are Fig.12 The schematic diagram of the internal interlayer electrodes and the outer side electrodes of the stacked piezoelectric ceramic column 223 is shown. The outer side electrodes are connected to the internal interlayer electrodes and can be divided into three groups of electrodes according to physical connection, one of which is grounded.

[0050] Fig.15 Schematic diagram of the driving method of the ultrasonic motor using the laminated piezoelectric ceramic column 223, and Fig.11 The driving method is similar. The polarization direction of the stacked piezoelectric ceramic column 223 is indicated by the symbols "+" and "-" (the single-layer ceramic is polarized along the thickness direction, from the "+" electrode to the "-" electrode).

[0051] Fig.16 The motor stator amplitude A changes with the driving voltage frequency f d The solid line is the axial component A of the L-mode amplitude of the stator friction head. z The dotted line is the component A of the B-mode amplitude of the stator friction head along the circumferential tangent θ . Drive frequency f d Slightly above the resonance frequency f L and f B , Δf is the available bandwidth of the driving frequency.

[0052] Fig.17 It is a schematic diagram that uses vectors to represent the relationship between the voltage applied to the piezoelectric element and the vibration mode. V1+V2 represents the voltage that excites the L-mode vibration mode, and V1-V2 represents the voltage that excites the B-mode vibration mode. According to the previous description, the two applied AC voltages have equal amplitudes, then the two vectors V1+V2 and V1-V2 will remain orthogonal (i.e., the phase difference is 90°). The amplitude of V1+V2 is The amplitude of V1-V2 is

[0053] Fig.18 The figure is a schematic diagram of the relationship between the motor stator amplitude and the driving voltage |V1+V2| and |V1-V2| (the driving frequency remains unchanged). The amplitude increases with the increase of voltage. The straight line segment in the figure reflects the linear proportional relationship in the low voltage range, and the amplitude gradually saturates in the high voltage range (not drawn in the figure). The solid line is the axial component A of the stator friction head L-mode amplitude z =k L (f) |V1+V2|, the dotted line is the component A of the B-mode amplitude of the stator friction head along the circumferential tangent θ =k B (f)|V1-V2|,k L (f) and k B (f) is a constant related to the driving frequency. Correspondingly, the motion trajectory of the end of the friction head is an ellipse, and its projection in the zθ plane is as follows: Fig.19 As shown. From the above analysis, it can be seen that by changing the amplitude V of the applied voltage and the frequency f d , and phase difference To adjust the amplitude of the friction head elliptical motion, thereby changing the driving force and speed of the motor. When the motor needs to run at a low speed, the vibration of the stator should be controlled so that the tangential amplitude A of the friction head θ Reduced while maintaining the amplitude of normal vibration A z , that is, it can maintain a large driving force while reducing the speed. In combination with the piezoelectric ultrasonic motor and driving method of the present invention, the voltage amplitude V and phase difference can be controlled. Keep It remains unchanged, that is, the amplitude of normal vibration can be maintained.

Claims

1. A rotary piezoelectric ultrasonic motor, comprising a stator, a rotor, and a bearing, characterized in that: The stator comprises a base, at least 6 rectangular cross-section columnar piezoelectric vibrators mounted on the upper surface of the base and evenly distributed along the circumferential direction, a protrusion is arranged on the upper end of each piezoelectric vibrator as a friction head, an axial through hole is arranged at the central position of the stator, and a bearing is installed in the through hole; The rotor comprises a rotating disk and a rotating shaft extending downward from the rotating disk, the rotating shaft is sleeved in a bearing, and the lower surface of the rotating disk contacts all friction heads on the stator; The stator has two vibration modes with approximately equal resonant frequencies, namely the B-mode mode and the L-mode mode; When in the B-mode, two adjacent piezoelectric vibrators perform bending vibrations in opposite directions; the bending direction is tangential to the circumference; When in the L-mode, two adjacent piezoelectric vibrators perform longitudinal expansion and contraction vibrations in opposite directions.

2. The rotary piezoelectric ultrasonic motor according to claim 1, characterized in that: Each piezoelectric vibrator has the same structure, and the piezoelectric vibrator includes a metal elastomer and two piezoelectric sheets respectively covering the inner and outer sides of the metal elastomer; the side of the piezoelectric sheet bonded to the metal elastomer is a fully covered inner surface electrode, and the side of the piezoelectric sheet facing away from the metal elastomer is two metal electrode areas separated in the middle, and the two metal electrode areas serve as the second electrode and the third electrode, and the parts of the piezoelectric sheet covered by the second electrode and the third electrode are polarized in the same direction along the thickness direction; the polarization directions of the two piezoelectric sheets of the same piezoelectric vibrator are opposite; the inner surface electrode is connected to the base as a ground electrode; when the second electrode and the third electrode are applied with an AC voltage of the same phase close to the resonance frequency, the stator L-mode mode is excited, and when the second electrode and the third electrode are applied with an AC voltage of opposite phase close to the resonance frequency, the stator B-mode mode is excited.

3. The rotary piezoelectric ultrasonic motor according to claim 1, characterized in that: Each of the piezoelectric vibrators has the same structure. The piezoelectric vibrator includes a laminated piezoelectric ceramic column formed by co-firing piezoelectric ceramics and metal electrodes and a friction head located at the top of the laminated piezoelectric ceramic column; the laminated piezoelectric ceramic column includes a plurality of sheet piezoelectric ceramics arranged side by side, a first electrode or an electrode group is sandwiched between two adjacent sheet piezoelectric ceramics, the electrode group includes a second electrode and a third electrode separated in the middle, a plurality of first electrodes and a plurality of electrode groups are interlaced and inserted between a plurality of sheet piezoelectric ceramics, wherein the first electrode is grounded, when the second electrode and the third electrode are applied with an AC voltage of the same phase close to the resonance frequency, the stator L-mode mode is excited, and when the second electrode and the third electrode are applied with an AC voltage of opposite phase close to the resonance frequency, the stator B-mode mode is excited.

4. The rotary piezoelectric ultrasonic motor according to any one of claims 2 or 3, characterized in that: The number of the columnar piezoelectric vibrators is an even number 2n, where n≥3.

5. A method for driving a rotary piezoelectric ultrasonic motor as claimed in any one of claims 2 to 4, characterized in that: The ground electrode is grounded, and the second electrode and the third electrode are respectively applied with an AC voltage V1=Vsin(2πf d t) and The friction head at the upper end of the piezoelectric vibrator produces a slight elliptical motion, and the rotor rotates due to the friction force; where V is the amplitude of the voltage, f d is the frequency, t is the time, is the phase difference.

6. The driving method according to claim 5, characterized in that: By changing the amplitude V and frequency f of the applied voltage d , and phase difference To adjust the amplitude of the elliptical motion of the friction head, thereby changing the driving force and speed of the motor.

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