Sandwich type piezoelectric two-degree-of-freedom mechanical arm and driving method thereof

Abstract

The invention discloses a sandwich type piezoelectric two-degree-of-freedom mechanical arm and a driving method thereof. The sandwich type piezoelectric two-degree-of-freedom mechanical arm comprises a plurality of unit arm sections connected in sequence. Each unit arm section comprises two piezoelectric vibrators and two joint parts; the spatial positions of the joint parts of the adjacent unit arm sections are mutually orthogonal, and orthogonal connection between the unit arm sections and application of pre-pressure are achieved through the joint parts between the unit arm sections. The invention has the advantages of compact and simple structure, no need of gear reduction and other mechanisms, easy sealing, easy realization of micronization, low operation noise, easy realization of low speed and large torque, no electromagnetic interference, power-off self-locking and high control precision.

Description

Technical Field

[0001] The invention relates to the field of piezoelectric drive and robots, in particular to a sandwich-type piezoelectric two-degree-of-freedom mechanical arm and a driving method thereof. Background Art

[0002] Existing traditional robotic arms use electromagnetic motors and hydraulic presses as driving sources to transmit the movement of the drivers to the driving joints through gears, pulleys, etc. They have complex structures, large sizes, and difficult to control speed accuracy. They are difficult to meet the use requirements for some special environment applications, such as deep sea, outer space, high electromagnetic interference, high temperature, and extremely cold environments, and it is difficult to achieve a miniaturized and compact design.

[0003] In recent years, piezoelectric-driven robotic arms have gradually emerged. They use the coupling of heterogeneous modes as the driving basis. During the design process, the modal frequency consistency adjustment is required, which is labor-intensive and complicated. In addition, many restrictions are imposed on the geometric shape and size of the structure, making it difficult to achieve serialization and modular design. In addition, the wear of this type of piezoelectric actuator during operation can cause two-phase frequency drift, increase the two-phase frequency difference, and reduce the driving performance of the robotic arm.

[0004] Therefore, in most of the current solutions, it is difficult to achieve miniaturization due to the complex structure of the robotic arm and its lack of compactness. Summary of the invention

[0005] In order to solve the problems of the prior art, the present invention provides a sandwich-type piezoelectric two-degree-of-freedom mechanical arm and a driving method thereof, which has a simple and compact design structure and is easy to realize miniaturization.

[0006] To achieve the above object, the embodiments of the present invention adopt the following technical solutions: In the first aspect, an embodiment of the present invention provides a sandwich-type piezoelectric two-degree-of-freedom mechanical arm, which is composed of at least two unit arm sections connected in sequence, and each unit arm section is connected by a connecting assembly; each unit arm section includes two piezoelectric vibrators and two joint parts; the piezoelectric vibrator includes: a first metal substrate, a second metal substrate and a piezoelectric drive assembly; the first metal substrate and the second metal substrate are both variable diameter cylinders, and the first metal substrate is provided with an external thread at one end close to the piezoelectric drive assembly, and the second metal substrate is provided with an internal thread at one end close to the piezoelectric drive assembly, and the external threads at both ends of the two piezoelectric vibrators of each unit arm section pass through the through holes on the two ear plates of the joint substrate and the through holes at both ends of the pressure plate spring in turn, and the threaded matching is completed by nuts and washers to realize the connection between the piezoelectric vibrator and the joint part; the piezoelectric drive assembly is installed from left to right in sequence: a first electrode sheet, a first piezoelectric ceramic sheet, a second electrode sheet, a second piezoelectric ceramic sheet, a third electrode sheet, The third piezoelectric ceramic sheet, the fourth electrode sheet, the fourth piezoelectric ceramic sheet and the fifth electrode sheet; the first electrode sheet, the third electrode sheet and the fifth electrode sheet of the piezoelectric drive assembly are grounded, and the second electrode sheet and the fourth electrode sheet input driving signals through the power supply; the joint part is composed of a joint base, a nut and a washer, one of the joint parts at both ends of the unit arm section is equipped with a pressure spring, the joint base is a semicircular hoop structure with a special circular cross-section, and through holes are provided at the two ear plates of the joint base; the joint part at one end of a unit arm section that is not equipped with a pressure spring is connected to the joint part at one end of another unit arm section that is equipped with a pressure spring; the joint bases of the joint parts of the two connected unit arm sections are orthogonally arranged in space, and the pressure spring plays a role in applying pre-pressure; the two orthogonally arranged joint bases are connected and positioned by nuts and washers and fixed to the two piezoelectric vibrators of their respective unit arm sections; the external threads at both ends of the piezoelectric vibrator are gap-matched with the through holes at the ear plates of the stator base; through holes corresponding to the two ear plates of the joint base are provided at both ends of the pressure spring.

[0007] In the first metal matrix: the diameter of the first stepped cylinder is greater than that of the second stepped cylinder; Along the axis direction of the first metal substrate, the length of the first stepped cylinder is smaller than that of the second stepped cylinder; for the second metal substrate, except for an internal thread matching the external thread at one end close to the piezoelectric drive component, the rest of the parts are exactly the same as the first metal substrate.

[0008] The first piezoelectric ceramic sheet, the second piezoelectric ceramic sheet, the third piezoelectric ceramic sheet and the fourth piezoelectric ceramic sheet are all single-partitioned annular piezoelectric ceramic sheets polarized along the thickness direction; in the single-partitioned annular piezoelectric ceramic sheets, the polarization directions of two adjacent piezoelectric ceramic sheets are opposite, that is, if the polarization direction of the first piezoelectric ceramic sheet is positive, the polarization directions of the second piezoelectric ceramic sheet and the fourth piezoelectric ceramic sheet are negative, and the polarization direction of the third piezoelectric ceramic sheet is positive, and vice versa.

[0009] The first piezoelectric ceramic sheet is in contact with one surface of the first electrode sheet and one surface of the second electrode sheet; the second piezoelectric ceramic sheet is in contact with the other surface of the second electrode sheet and one surface of the third electrode sheet; the third piezoelectric ceramic sheet is in contact with the other surface of the third electrode sheet and one surface of the fourth electrode sheet; the fourth piezoelectric ceramic sheet is in contact with the other surface of the fourth electrode sheet and one surface of the fifth electrode sheet; the surfaces of the first electrode sheet and the fifth electrode sheet that are not in contact with the piezoelectric ceramic sheet are in contact with the end surface of the first stepped cylinder of the first metal substrate and the end surface of the first stepped cylinder of the second metal substrate, respectively; The first electrode sheet, the second electrode sheet, the third electrode sheet, the fourth electrode sheet and the fifth electrode sheet are all annular electrode sheets with a round ear.

[0010] The external threads at both ends of the two piezoelectric vibrators of the unit arm section pass through the through holes at the ear plate of the joint base, the through holes at both ends of the pressure spring, and the washers in sequence, and then the piezoelectric vibrator and the joint part are assembled and fixedly connected through the nut and the external threads at both ends of the piezoelectric vibrator.

[0011] The piezoelectric drive components are insulated with waterproof glue.

[0012] In a second aspect, an embodiment of the present invention provides a driving process of a sandwich-type piezoelectric two-degree-of-freedom mechanical arm, comprising: A simple harmonic driving signal is applied to the second electrode plate and the fourth electrode plate of the piezoelectric driving assembly of the two piezoelectric vibrators on the unit arm section, so that the points where the unit arm section joint matrix of the piezoelectric vibrator to which the simple harmonic driving signal is applied contacts with the joint matrix of the adjacent unit arm section connected in series produce elliptical motion.

[0013] The harmonic driving signal applied to the two piezoelectric vibrators of the same unit arm section is a harmonic driving signal of a specific frequency with a time phase difference of π / 2, wherein the specific frequency is a preset frequency value, and simultaneously stimulates the first-order longitudinal vibration mode of the two piezoelectric vibrators with a time phase difference of π / 2.

[0014] Apply driving signals to two piezoelectric vibrators of adjacent unit arm sections respectively, triggering the rotation of the unit arm sections around the axis direction of the circular cross-section of the contact part of the joint base of the adjacent unit arm section; apply driving signals to the piezoelectric vibrators of the two unit arm sections respectively, triggering the two unit arm sections to rotate in two degrees of freedom in orthogonal planes, wherein the unit arm section and the adjacent unit arm section are orthogonal in space.

[0015] The beneficial effects of the present invention are: 1. Aiming at the problems of complex structure and low control precision of traditional electromagnetic and hydraulic driven mechanical arms, the present invention has a compact and simple structure, does not require gear reduction mechanisms, is easy to seal, is easy to achieve miniaturization, has low operating noise, is easy to achieve low-speed and high torque, is not subject to electromagnetic interference, can self-lock when powered off, and has high control precision.

[0016] 2. Compared with other piezoelectrically actuated robotic arms, since the piezoelectric vibrator uses the first-order longitudinal vibration single mode as the driving basis, there is no need to adjust the frequency consistency of the special-shaped modes, which reduces the restrictions on the design size and shape of the robotic arm, and is easier to achieve serialized and modular design. In addition, the robotic arm has many adjustable sizes depending on the engineering application scenario, has strong engineering applicability, and has important application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of a sandwich-type piezoelectric two-degree-of-freedom mechanical arm provided by an embodiment of the present invention; Figure 2 A schematic diagram of a unit arm section structure provided by an embodiment of the present invention; Figure 3 A schematic diagram of the structure of a piezoelectric vibrator provided in an embodiment of the present invention; Figure 4 A schematic diagram of a metal substrate of a piezoelectric vibrator provided in an embodiment of the present invention; Figure 5 A schematic diagram of a piezoelectric drive assembly provided in an embodiment of the present invention; Figure 6 A schematic diagram of the structure of a joint part provided by an embodiment of the present invention; Figure 7 A schematic diagram of a voltage signal applied to a piezoelectric drive assembly provided in an embodiment of the present invention; Figure 8 A schematic diagram of the first-order longitudinal vibration mode of a piezoelectric vibrator along the Z axis provided by an embodiment of the present invention; The reference numerals in the accompanying drawings represent: 1-first unit arm section, 2-second unit arm section, 3-third unit arm section, 4-piezoelectric vibrator, 5-joint portion, 4.1-first metal substrate, 4.2-piezoelectric drive assembly, 4.3-second metal substrate, 4.1.1-first metal substrate first stepped cylinder, 4.1.2-first metal substrate second stepped cylinder, 4.1.3 first metal substrate inner outer thread, 4.3.1-second metal substrate first stepped cylinder, 4.3.2-second metal substrate The second stepped cylinder, 4.3.3 the inner thread of the second metal matrix, 4.2.1-the first piezoelectric ceramic sheet, 4.2.2-the second piezoelectric ceramic sheet, 4.2.3-the third piezoelectric ceramic sheet, 4.2.4-the fourth piezoelectric ceramic sheet, 4.2.5-the first electrode sheet, 4.2.6-the second electrode sheet, 4.2.7-the third electrode sheet, 4.2.8-the fourth electrode sheet, 4.2.9-the fifth electrode sheet, 5.1-the joint matrix, 5.2-the nut, 5.3-the washer, 5.4-the compression spring. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Specific as Figure 1 As shown, the present invention discloses a sandwich-type piezoelectric two-degree-of-freedom robotic arm, comprising a plurality of sequentially connected unit arm sections and connecting components between the arm sections; for the purpose of illustration, a two-degree-of-freedom piezoelectric driven robotic arm comprising three unit arm sections is taken as an example, and the three unit arm sections comprised are respectively a first unit arm section 1, a second unit arm section 2, and a third unit arm section 3.

[0021] like Figure 2 As shown, each unit arm segment includes two piezoelectric vibrators 4 and two joint parts 5.

[0022] like Figure 3 Each piezoelectric vibrator 4 shown comprises a first metal substrate 4.1, a second metal substrate 4.3 and a piezoelectric driving component 4.2.

[0023] like Figure 4The first metal substrate 4.1 shown is a variable diameter cylinder with external threads at both ends, wherein the external thread 4.1.3 on the side close to the piezoelectric drive component 4.2 is threadedly matched with the internal thread 4.3.3 of the second metal substrate 4.3, and the second metal substrate 4.3 is a variable diameter cylinder with an internal thread 4.3.3 on one end close to the piezoelectric drive component 4.2 and an external thread on the other end. The first metal substrate 4.1 and the second metal substrate 4.3 are completely identical except for the internal and external threads for matching connection at one end close to the piezoelectric drive component 4.2. The first metal substrate is used as an example for explanation. The diameter of the first stepped cylinder 4.1.1 of the first metal substrate 4.1 is larger than that of the second stepped cylinder 4.1.2, and along the axis of the first metal substrate 4.1 (or Figure 8 In the Z-axis direction, the length of the first stepped cylinder 4.1.1 is smaller than the length of the second stepped cylinder 4.1.2.

[0024] like Figure 5 The piezoelectric drive assembly 4.2 shown includes, from left to right, a first electrode sheet 4.2.5, a first piezoelectric ceramic sheet 4.2.1, a second electrode sheet 4.2.6, a second piezoelectric ceramic sheet 4.2.2, a third electrode sheet 4.2.7, a third piezoelectric ceramic sheet 4.2.3, a fourth electrode sheet 4.2.8, a fourth piezoelectric ceramic sheet 4.2.4 and a fifth electrode sheet 4.2.9; the first to fourth piezoelectric ceramic sheets are all single-zone annular piezoelectric ceramic sheets polarized along the thickness direction, and the polarization directions of two adjacent piezoelectric ceramic sheets are opposite, that is, if the polarization direction of the first piezoelectric ceramic sheet 4.2.1 is positive, then the polarization directions of the second piezoelectric ceramic sheet 4.2.2 and the fourth piezoelectric ceramic sheet 4.2.4 are negative, and the polarization direction of the third piezoelectric ceramic sheet 4.2.3 is positive, and vice versa; the first to fourth electrode sheets are all circular sheets with a small round ear. Annular electrode sheet; the first piezoelectric ceramic sheet 4.2.1 is in contact with one surface of the first electrode sheet 4.2.5 and one surface of the second electrode sheet 4.2.6; the second piezoelectric ceramic sheet 4.2.2 is in contact with the other surface of the second electrode sheet 4.2.6 and one surface of the third electrode sheet 4.2.7; the third piezoelectric ceramic sheet 4.2.3 is in contact with the other surface of the third electrode sheet 4.2.7 and one surface of the fourth electrode sheet 4.2.8; the fourth piezoelectric ceramic sheet 4.2.4 is in contact with the other surface of the fourth electrode sheet 4.2.8 and one surface of the fifth electrode sheet 4.2.9; the surfaces of the first electrode sheet 4.2.5 and the fifth electrode sheet 4.2.9 that are not in contact with the piezoelectric ceramic sheets are in contact with the end surface of the first stepped cylinder 4.1.1 of the first metal substrate and the end surface of the first stepped cylinder 4.3.1 of the second metal substrate, respectively.

[0025] like Figure 6As shown, the joint part 5 is composed of a joint base 5.1, a nut 5.2 and a washer 5.3. One of the joint parts 5 at both ends of the unit arm section is equipped with a pressure spring 5.4. The joint base 5.1 is a semicircular hoop structure with a special circular cross-section. Through holes are arranged at the two ear plates of the joint base 5.1. The joint part 5 at one end of a unit arm section not equipped with a pressure spring 5.4 is connected to the joint part 5 at one end of another unit arm section equipped with a pressure spring 5.4. The joint bases 5.1 of the joint parts 5 of the two connected unit arm sections are orthogonally arranged in space, and the pressure spring 5.4 plays a role in applying pre-pressure. The two orthogonally arranged joints The joint base 5.1 is connected and positioned by a nut 5.2 and a washer 5.3 and fixed to the two piezoelectric vibrators 4 of each unit arm section; the external threads at both ends of the piezoelectric vibrator 4 are gap-matched with the through holes at the ear plate of the stator base 5.1; through holes corresponding to the two ear plates of the joint base 5.1 are provided at both ends of the pressure leaf spring 5.4, and the external threads at both ends of the two piezoelectric vibrators 4 of the unit arm section pass through the through holes at the ear plate of the joint base 5.1, the through holes at both ends of the pressure leaf spring 5.4, and the washer 5.3 in sequence, and then the piezoelectric vibrator 4 and the joint part 5 are assembled and fixedly connected by the nut 5.2 and the external threads at both ends of the piezoelectric vibrator 4.

[0026] like Figure 7 As shown, a simple harmonic driving signal is applied to the second electrode sheet 4.2.6 and the fourth electrode sheet 4.2.8 of the piezoelectric driving assembly 4.2 of the two piezoelectric vibrators 4 on the unit arm section. The simple harmonic driving signal applied to the two piezoelectric vibrators 4 of the same unit arm section is a simple harmonic driving signal of a specific frequency with a time phase difference of π / 2, wherein the specific frequency is a preset frequency value, and simultaneously stimulates the two piezoelectric vibrators 4 to have a time phase difference of π / 2 as shown in FIG. Figure 8 The first-order longitudinal vibration mode shown causes each contact point between the unit arm joint base 5.1 of the piezoelectric vibrator 4 to which a simple harmonic driving signal is applied and the joint base 5.1 of the adjacent unit arm section connected in series to produce a slight elliptical motion, generating a driving force through friction.

[0027] When working, driving signals can be applied to the two piezoelectric vibrators 4 of the adjacent unit arm sections respectively, triggering the rotation of the unit arm sections around the axis direction of the circular cross section of the contact part of the joint base 5.1 of the adjacent unit arm section. Applying driving signals to the piezoelectric vibrators 4 of the two unit arm sections respectively can trigger the two-degree-of-freedom rotation of the two unit arm sections in the orthogonal plane, wherein the unit arm section and the adjacent unit arm section are orthogonal in space.

[0028] Since the unit arm section and its adjacent unit arm section are orthogonal in space, applying driving signals to the corresponding piezoelectric vibrators of the two unit arm sections can realize two-degree-of-freedom rotation of the two unit arm sections in the orthogonal plane.

[0029] In the present embodiment, a sandwich-type piezoelectric two-degree-of-freedom mechanical arm and a driving method thereof are disclosed. The mechanical arm comprises a plurality of sequentially connected unit arm sections and connection components between the arm sections; each unit arm section comprises two piezoelectric vibrators 4 and a joint portion 5; the spatial positions of the joint portions 5 of each unit arm section and the adjacent unit arm section are mutually orthogonal, and two orthogonally arranged joint bases 5.1 are connected and positioned by nuts 5.2 and washers 5.3 and fixed to the two piezoelectric vibrators 4 of their respective unit arm sections, and a compression spring 5.4 serves to apply pre-pressure; during operation, the simple harmonic driving signal applied to the two piezoelectric vibrators of the same unit arm section is a simple harmonic driving signal of a specific frequency with a time phase difference of π / 2, wherein the specific frequency is a preset The frequency value can simultaneously excite the first-order longitudinal vibration mode of the two piezoelectric vibrators 4 with a phase difference of π / 2 in time, so that the points where the unit arm section joint matrix 5.1 of the piezoelectric vibrator 4 to which the simple harmonic driving signal is applied and the joint matrix 5.1 of the adjacent unit arm section in series produce a slight elliptical motion, and a driving force is generated through the friction effect. The driving signal is applied to the two piezoelectric vibrators 4 of the adjacent unit arm sections, respectively, and the rotation of the unit arm section around the axis direction of the circular section of the contact part of the joint matrix 5.1 of the adjacent unit arm section is triggered. Since the unit arm section and its adjacent unit arm section are orthogonal in space, the corresponding piezoelectric vibrators are applied with the driving signal to the two unit arm sections, so that the two unit arm sections can realize the two-degree-of-freedom rotation of the two unit arm sections in the orthogonal plane.

[0030] The piezoelectric vibrator 4 of the present invention uses the first-order longitudinal vibration single mode as the driving basis, and there is no need to adjust the frequency consistency of the special-shaped mode, which reduces the restrictions on the design size and shape of the robot arm, and is easier to achieve serialized and modular design. It has important application prospects in different engineering applications.

[0031] Compared with the prior art, this embodiment has the following advantages: Compared with traditional electromagnetic and hydraulic machine-driven mechanical arms, it has a simple structure, light weight, no need for gear reduction mechanisms, is easy to seal, easy to achieve miniaturization, has low operating noise, is easy to achieve low-speed and high torque, is not affected by electromagnetic interference, can self-lock when power is off, and has high control accuracy.

[0032] Compared with other piezoelectrically actuated robotic arms, since the piezoelectric vibrator 4 uses the first-order longitudinal vibration single mode as the driving basis, there is no need to adjust the modal coupling frequency consistency of different phase modes, which reduces the restrictions on the design size and shape of the robotic arm, and is easier to achieve serialized and modular design. Moreover, depending on the engineering application scenario, the robotic arm has many adjustable sizes, strong engineering applicability, and important application prospects.

[0033] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, the above is only a preferred embodiment of the present invention. Since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited to this. Any technician familiar with the technical field is within the technical scope disclosed by the present invention. For ordinary technicians in the technical field, changes or replacements that can be easily thought of should be covered within the protection scope of the present invention without departing from the principle of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A sandwich-type piezoelectric two-degree-of-freedom robotic arm, characterized in that: It comprises at least two sequentially connected unit arm sections, wherein adjacent unit arm sections are connected via joint sections (5), and each unit arm section comprises two piezoelectric vibrators (4) and two joint sections (5) respectively located at two ends of the piezoelectric vibrators; The piezoelectric vibrator (4) comprises a first metal substrate (4.1), a piezoelectric drive assembly (4.2) and a second metal substrate (4.3) which are connected in sequence via a threaded structure, wherein the first metal substrate (4.1) and the second metal substrate (4.3) are both cylinders with variable diameters, and the piezoelectric drive assembly (4.2) is installed with the following components in sequence from left to right: a first electrode sheet (4.2.5), a first piezoelectric ceramic sheet (4.2.1), a second electrode sheet (4.2.6), a second piezoelectric ceramic sheet (4.2.7), a second electrode sheet (4.2.8), a second electrode sheet (4.2.9), a second electrode sheet (4.30), a second electrode sheet (4.31), a second electrode sheet (4.32), a second electrode sheet (4.33), a second electrode sheet (4.34), a second electrode sheet (4.35), a second electrode sheet (4.36), a second electrode sheet (4.37), a second electrode sheet (4.38), a second electrode sheet (4.39), a second electrode sheet (4.40), a second electrode sheet (4.41), a second electrode sheet (4.42), a second electrode sheet (4.43), a second electrode sheet (4.44), a second electrode sheet (4.45), a second electrode sheet (4.46), a second electrode sheet (4.47), a second electrode sheet (4.48), a second electrode sheet (4.49), a second electrode sheet (4.50), a first electrode sheet (4.51), a first electrode sheet (4.52), a second electrode sheet (4.53), a second electrode sheet (4.54), a second electrode sheet (4.55), a first electrode sheet (4.56), a second electrode sheet (4.57), a second electrode sheet (4.58), a first electrode sheet (4.59), a first electrode sheet (4.59), a first electrode sheet (4.59), a first electrode sheet (4.5 2.2), a third electrode sheet (4.2.7), a third piezoelectric ceramic sheet (4.2.3), a fourth electrode sheet (4.2.8), a fourth piezoelectric ceramic sheet (4.2.4) and a fifth electrode sheet (4.2.9); the first electrode sheet (4.2.5), the third electrode sheet (4.2.7) and the fifth electrode sheet (4.2.9) of the piezoelectric drive assembly (4.2) are grounded, and the second electrode sheet (4.2.6) and the fourth electrode sheet (4.2.8) are driven by a power supply input signal; The joint part (5) is a joint base (5.1) of a semicircular hoop structure with a special-shaped circular cross-section. Through holes are provided at two ear plates of the joint base (5.1). The first metal base (4.1) and the second metal base (4.3) of the piezoelectric vibrator (4) are respectively fixedly connected to the joint bases (5.1) at both ends. One of the joint parts (5) at both ends of the unit arm section is equipped with a compression spring (5.4). In two adjacent unit arm sections, the joint part (5) at one end not equipped with a compression spring (5.4) is connected to the joint part (5) at one end of the other unit arm section equipped with a compression spring (5.4). The joint bases (5.1) of the joint parts (5) of the two connected unit arm sections are orthogonally arranged in space, and the compression spring (5.4) applies pre-pressure to the two joint bases (5.1).

2. The sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 1, characterized in that: The first metal matrix (4.1) comprises a first stepped cylinder (4.1.1) and a second stepped cylinder (4.1.2); the diameter of the first stepped cylinder (4.1.1) is greater than that of the second stepped cylinder (4.1.2) along the axis of the first metal matrix (4.1); and the length of the first stepped cylinder (4.1.1) is less than that of the second stepped cylinder (4.1.2).

3. The sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 1, characterized in that: The first piezoelectric ceramic sheet (4.2.1), the second piezoelectric ceramic sheet (4.2.2), the third piezoelectric ceramic sheet (4.2.3) and the fourth piezoelectric ceramic sheet (4.2.4) are all single-partitioned annular piezoelectric ceramic sheets polarized along the thickness direction; among the above-mentioned piezoelectric ceramic sheets, the polarization directions of two adjacent piezoelectric ceramic sheets are opposite.

4. The sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 3, characterized in that: The first piezoelectric ceramic sheet (4.2.1) is in contact with one surface of the first electrode sheet (4.2.5) and one surface of the second electrode sheet (4.2.6); The second piezoelectric ceramic sheet (4.2.2) contacts the other surface of the second electrode sheet (4.2.6) and one surface of the third electrode sheet (4.2.7); The third piezoelectric ceramic sheet (4.2.3) is in contact with the other surface of the third electrode sheet (4.2.7) and one surface of the fourth electrode sheet (4.2.8); The fourth piezoelectric ceramic sheet (4.2.4) contacts the other surface of the fourth electrode sheet (4.2.8) and one surface of the fifth electrode sheet (4.2.9); The first electrode sheet (4.2.5) and the fifth electrode sheet (4.2.9) are respectively connected to the first stepped cylinder ( 4.1.1) contacts the end face of the first stepped cylinder (4.3.1) of the second metal matrix.

5. The sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 1 or 4, characterized in that: The first electrode sheet (4.2.5), the second electrode sheet (4.2.6), the third electrode sheet (4.2.7), the fourth electrode sheet (4.2.8) and the fifth electrode sheet (4.2.9) are all circular ring-shaped electrode sheets with a round ear.

6. The sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 1, characterized in that: The two piezoelectric vibrators (4) of the unit arm section are provided with external threads at both ends, and the external threads sequentially pass through the through holes at the ear plate of the joint base (5.1) and the through holes at both ends of the pressure plate spring (5.4), and then the piezoelectric vibrator (4) and the joint part (5) are assembled and fixedly connected by a nut (5.2) and the external threads at both ends of the piezoelectric vibrator (4), and a washer (5.3) is provided between the pressure plate spring (5.4) and the nut (5.2).

7. The sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 1, characterized in that: The piezoelectric drive component (4.2) is insulated using waterproof glue.

8. A method for driving the sandwich-type piezoelectric two-degree-of-freedom mechanical arm as claimed in any one of claims 1 to 7, characterized in that The following steps are involved: A simple harmonic drive signal is applied to the second electrode sheet (4.2.6) and the fourth electrode sheet (4.2.8) of the piezoelectric drive assembly (4.2) of the two piezoelectric vibrators (4) on the unit arm section, so that each point where the unit arm section joint base (5.1) of the piezoelectric vibrator (4) to which the simple harmonic drive signal is applied contacts with the joint base (5.1) of the adjacent unit arm section connected in series generates an elliptical motion.

9. The driving method of the sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 8, characterized in that: The simple harmonic driving signal applied to the two piezoelectric vibrators of the same unit arm section is a simple harmonic driving signal of a specific frequency with a time phase difference of π / 2, wherein the specific frequency is a preset frequency value, and simultaneously stimulates the two piezoelectric vibrators (4) to have a first-order longitudinal vibration mode with a time phase difference of π / 2.

10. The driving method of the sandwich-type piezoelectric two-degree-of-freedom mechanical arm according to claim 8, characterized in that: A driving signal is applied to two piezoelectric vibrators (4) of adjacent unit arm sections respectively, triggering the rotation of the unit arm sections around the axis direction of the circular cross section of the contact portion of the joint base (5.1) of the adjacent unit arm section; a driving signal is applied to the piezoelectric vibrators (4) of the two unit arm sections respectively, triggering the two unit arm sections to rotate in two degrees of freedom in an orthogonal plane, wherein the unit arm section and the adjacent unit arm section are orthogonal in space.

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