Three-directional excitation force measuring device and measuring method for piezoelectric decoupled thruster

Abstract

The application provides a piezoelectric decoupling type thruster three-direction excitation force measuring device and measuring method, relates to the technical field of propeller excitation force measurement, and comprises a three-direction piezoelectric force sensor, a propeller and a transmission shaft. One end of the three-direction piezoelectric force sensor is connected with the propeller, the other end of the three-direction piezoelectric force sensor is connected with the transmission shaft, and the three-direction piezoelectric force sensor is installed inside the transmission shaft. The three-direction piezoelectric force sensor measures unsteady hydrodynamic force or unsteady aerodynamic force of the propeller in the longitudinal direction, the transverse direction and the vertical direction. The application adopts a force measuring disc with a thin plate configuration and a measuring rod with a rod configuration, decouples the radial excitation of the propeller and the longitudinal excitation, measures three-direction excitation force of the propeller installed at the front end of the transmission shaft through the piezoelectric force sensor, occupies a small space, and can directly measure the three-direction unsteady excitation force of the propeller in a complex environment.

Description

Technical Field

[0001] This invention relates to the field of propeller excitation force measurement technology, specifically to a piezoelectric decoupled propeller three-dimensional excitation force measurement device and method. Background Technology

[0002] Vibration and noise caused by the propulsion system are major components of the total noise of a ship. Measuring the unsteady excitation force of the propeller in all directions is crucial for the low-noise design and vibration control of ships. Therefore, it is necessary to design a sensor for measuring the triaxial excitation force of underwater propellers.

[0003] Existing triaxial piezoelectric force sensors cannot be directly used to measure unsteady excitation forces of propellers because when embedded inside the shaft system, the sensor and the thin wall of the hollow shaft system will have a strong coupling effect. The measured force results in each direction will be coupled together. For example, when the sensor is subjected to a longitudinal force, its lateral and vertical response signals will also be strong, making it impossible to accurately obtain the unsteady excitation forces in each direction experienced by the propeller. Devices that can directly measure the unsteady excitation forces in each direction of the propeller are almost non-existent. This is mainly because the environment in which propellers operate is harsh, making direct measurement difficult. Furthermore, the unsteady excitation forces in each direction have a wide dynamic range and rich spectral components, and their amplitude is much smaller than that of static thrust. The measured responses in each direction are easily coupled together and difficult to distinguish.

[0004] Patent document CN104316229A discloses a composite measuring device for dynamic thrust and torque of a propeller. Developing a measuring device that can simultaneously and accurately measure the dynamic thrust and torque generated by propeller rotation is of significant importance. The composite measuring device for dynamic thrust and torque of a propeller comprises: a propeller, a main shaft, a bearing housing, and a tension / compression sensor. The propeller has a main shaft, the end of which passes through the bearing housing and is coaxially connected to the output shaft of a drive motor via a dynamic torque sensor. A tension / compression sensor is mounted on the bearing housing, and the sensor is connected to a base plate via a connector. The bearing housing and the base plate are slidably connected. This invention applies to the composite measuring device for dynamic thrust and torque of a propeller; however, the sensor in this design fails to accurately measure the lateral and vertical unsteady excitation forces acting on the propeller, which is detrimental to further research on ship vibration reduction and noise reduction. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a piezoelectric decoupled thruster three-dimensional excitation force measuring device and method.

[0006] According to the present invention, a piezoelectric decoupled propeller triaxial excitation force measuring device includes: a triaxial piezoelectric force sensor, a propeller and a drive shaft, one end of the triaxial piezoelectric force sensor is connected to the propeller, the other end of the triaxial piezoelectric force sensor is connected to the drive shaft, and the triaxial piezoelectric force sensor is installed inside the drive shaft.

[0007] The triaxial piezoelectric force sensor measures unsteady hydrodynamic or unsteady aerodynamic forces on the propeller in the longitudinal, lateral, and vertical directions.

[0008] Preferably, the drive shaft includes a mounting shaft and a long shaft, with a clearance fit between the mounting shaft and the long shaft, and the triaxial piezoelectric force sensor is disposed inside the hollow structure formed by the mounting shaft and the long shaft;

[0009] The mounting shaft and the long shaft have hollow interiors. The lower end face of the hollow mounting shaft has a stepped shaft structure, and the upper end face of the hollow long shaft has a stepped shaft structure. The lower end face of the mounting shaft and the upper end face of the long shaft are clearance-fitted through the stepped shaft structure, and the mounting shaft and the long shaft are fixedly connected by bolts.

[0010] Preferably, the triaxial piezoelectric force sensor includes a stepped fixed shaft, a force measuring disk, an adapter shaft, and a force measuring rod. One end of the adapter shaft is connected to the force measuring rod, and the other end of the adapter shaft is connected to the stepped fixed shaft. The force measuring disk is interference-fitted and fixed in the middle of the adapter shaft.

[0011] The force-measuring disk contacts the inner wall of the mounting shaft, and the force-measuring disk transmits the force radially along the disk surface, thus achieving decoupling of the triaxial piezoelectric force sensor.

[0012] Preferably, the force measuring rod has a thin rod structure in the middle, and the force measuring rod transmits the longitudinal force on the propeller through the thin rod structure;

[0013] Both the upper and lower ends of the force measuring rod are set as threaded shaft sections. The upper end of the force measuring rod is fixed to the inner end face of the mounting shaft through the threaded structure, and the lower end of the force measuring rod is connected to the upper end of the adapter shaft through the threaded structure.

[0014] Preferably, the thickened portion around the force measuring plate is fixed to the stepped end face of the mounting shaft by evenly distributed screws.

[0015] Preferably, multiple piezoelectric ceramic sheets are fitted onto the stepped fixed shaft with a clearance fit, and the stepped fixed shaft is pressed by the lower end face of the adapter shaft. The piezoelectric ceramic sheets are fixedly connected to the inner end face of the long shaft by threads.

[0016] The piezoelectric ceramic sheet is ring-shaped, and multiple piezoelectric ceramic sheets convert the longitudinal dynamic force, lateral dynamic force and vertical dynamic force on the propeller into electrical signals respectively.

[0017] Preferably, the propeller includes a hub, blades, and a hub cap. The hub and blades are fixed together. The hub is mounted on the mounting shaft by a threaded structure and is fixed by the hub cap.

[0018] The present invention also provides a measurement method using a piezoelectric decoupled thruster triaxial excitation force measuring device, comprising the following steps:

[0019] S1: To install a triaxial piezoelectric force sensor, first mate the force measuring rod with the adapter shaft, then install the force measuring disk on the adapter shaft with an interference fit, then fix all three to the mounting shaft, and connect the force measuring disk to the mounting shaft with four evenly distributed screws, denoted as assembly a;

[0020] The piezoelectric ceramic sheet, the stepped fixed shaft, and the long shaft are fixedly connected and denoted as assembly b;

[0021] Finally, assembly a and assembly b are connected by a threaded structure of the adapter shaft and the stepped fixed shaft, and the mounting shaft is fastened to the long shaft by bolts.

[0022] S2: Experimentally calculate the equivalent longitudinal stiffness, equivalent lateral stiffness, and equivalent vertical stiffness of the triaxial piezoelectric force sensor and the combined effect of the triaxial piezoelectric force sensor and the hollow tube wall of the drive shaft. Calculate the measurement scaling factors of the longitudinal, lateral, and vertical excitation forces as parameters.

[0023] S3: Controls the propeller to start working, and the propeller is subjected to dynamic excitation force;

[0024] S4: The dynamic excitation force is converted into a response signal by a triaxial piezoelectric force sensor, and the response signal is input into the PC through the LMS data acquisition system;

[0025] S5: The PC processes the input signal based on the measurement scaling factor obtained in step S2, thereby reconstructing the dynamic excitation force.

[0026] Preferably, in step S2, the triaxial piezoelectric force sensor is connected in parallel with the tube wall of the mounting shaft and the hollow structure of the long shaft;

[0027] The equivalent longitudinal stiffness of the combined action of the triaxial piezoelectric force sensor and the tube wall is calculated. It is equivalent to the longitudinal stiffness of the hollow shaft thin wall combined with the longitudinal stiffness of the triaxial piezoelectric force sensor. The equivalent longitudinal stiffness of the hollow shaft thin wall is:

[0028]

[0029] Among them, E t Let A be the elastic modulus of the drive shaft. t l is the cross-sectional area of ​​the hollow shaft of the drive shaft. t The length of the hollow section consisting of the mounting shaft, connecting shaft, and long shaft;

[0030] The longitudinal equivalent stiffness of the triaxial piezoelectric force sensor was measured to be k through experiments. z Therefore, the total equivalent longitudinal stiffness of the embedded triaxial piezoelectric force sensor and the tube wall is:

[0031]

[0032] And k x With k t With forces of similar magnitude, the hollow portion of the drive shaft shares the force of the triaxial piezoelectric force sensor; the longitudinal measurement scaling factor is calculated as follows:

[0033] α x =k1 / k x

[0034] Similarly, the scale factors for lateral and vertical measurements are calculated using α. y With α z express.

[0035] Preferably, in step S5, the response signal is input into the PC through the LMS data acquisition system, and the input signal is processed by measuring the scaling factor. The calculation formulas for the three-dimensional unsteady excitation forces are as follows:

[0036] Longitudinal force:

[0037] F x =α x *f x

[0038] Lateral force:

[0039] F y =α y *f y

[0040] Vertical force:

[0041] F z =α z *f z

[0042] Among them, f x f y with f z The results show the longitudinal, lateral, and vertical response measurements of the triaxial piezoelectric force sensor.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The present invention has a simple structure and is easy to operate. It can completely measure the proportional factor through experimental calculation, enabling the direct measurement of the three-dimensional unsteady excitation force of the propeller through a piezoelectric force sensor in complex environments.

[0045] (2) The present invention is located close to the propeller, and the measured signal has a high signal-to-noise ratio. In addition, the present invention occupies little space, is easy to adjust, and has strong applicability.

[0046] (3) The present invention uses the principle of unidirectional force transmission of thin rod and thin disk to transmit unsteady excitation forces in the longitudinal, transverse and vertical directions respectively, avoiding the strong coupling effect of the shaft wall caused by the ordinary triaxial piezoelectric sensor when it is embedded in the transmission shaft.

[0047] (4) The annular ceramic piezoelectric sheet set in the triaxial piezoelectric force sensor used in this invention can be used to measure dynamic force and has the characteristics of high piezoelectric performance, good stability, high frequency response and good durability. Attached Figure Description

[0048] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0049] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0050] Figure 2 This is a partial schematic diagram of the long axis and the stepped fixed axis in this invention;

[0051] Figure 3 This is a schematic diagram of the structure of the triaxial piezoelectric force sensor in the invention;

[0052] Figure 4 This is a flowchart of step S2 in Embodiment 2 of the present invention;

[0053] Figure 5 This is a flowchart of step S5 in Embodiment 2 of the present invention.

[0054] The figure shows: 1. Hub, 2. Blade, 3. Blade mounting shaft, 4. Hub cap, 5. Long shaft, 6. Stepped fixing shaft, 7. Force measuring disk, 8. Adapter shaft, 9. Force measuring rod, 10. Through hole, 11. Piezoelectric ceramic plate, and 12. Triaxial piezoelectric force sensor. Detailed Implementation

[0055] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0056] Example 1

[0057] This invention provides a piezoelectric decoupled thruster three-dimensional excitation force measuring device, such as... Figure 1-3 As shown, the system includes a propeller hub 1, propeller blades 2, a hub cap 4, a propeller mounting shaft 3, a long shaft 5, and a triaxial piezoelectric force sensor 12. The propeller hub 1 and the propeller blades 2 are fixedly connected as a single structure. The propeller hub 1 is mounted on the propeller mounting shaft 3 via a threaded structure and is fixed by the hub cap 4. The mounting shaft 3 and the long shaft 5 form a drive shaft, both of which have hollow internal structures. The triaxial piezoelectric force sensor 12 is installed inside the drive shaft and is used to measure the unsteady hydrodynamic or unsteady aerodynamic forces acting on the propeller in the longitudinal, lateral, and vertical directions to prevent damage from extreme environments. One end of the triaxial piezoelectric force sensor 12 is close to the propeller hub 1 and the propeller blades 2, providing a high signal-to-noise ratio, while the other end is fixedly connected to the long shaft 5 to improve the rigidity of the measurement system itself.

[0058] The mounting shaft 3 has a hollow structure inside, with a stepped shaft structure at the lower end of the hollow section. The long shaft 5 also has a hollow structure inside, with a stepped shaft structure at the upper end. The mounting shaft 3 and the long shaft 5 are fitted together with a clearance fit and fixedly connected by bolts. The triaxial piezoelectric force sensor 12 is installed inside the hollow structure formed by the mounting shaft 3 and the long shaft 5. When installing the triaxial piezoelectric force sensor 12, the triaxial piezoelectric force sensor 12 and the drive shaft are divided into two parts: assembly a and assembly b. Assembly a includes a force measuring disk 7, a connecting shaft 8, a force measuring rod 9, and the mounting shaft 3. Assembly b includes a stepped fixed shaft 6, a piezoelectric ceramic plate 11, and the long shaft 5. Assembly a and assembly b are fitted together by the threaded structure of the connecting shaft 8 and the stepped fixed shaft 6, and the mounting shaft 3 and the long shaft 5 are fastened together by bolts to seal the shaft system, ensure the integrity of the drive shaft, and prevent the sensor from being damaged by extreme environments. To ensure the reliability of the connection between assembly a and assembly b, the rotation direction of the propeller and the shaft system must be opposite to the direction of the connecting threads of assembly a and assembly b.

[0059] The triaxial piezoelectric force sensor 12 includes a stepped fixed shaft 6, a force-measuring disk 7, a connecting shaft 8, a force-measuring rod 9, and a piezoelectric ceramic plate 11. The upper end of the force-measuring rod 9 is fixedly connected to the inner end face of the mounting shaft 3 via a threaded structure. The middle of the force-measuring rod 9 is a thin rod structure, which can only transmit the longitudinal force it receives and cannot transmit radial force or torque. Therefore, the thin rod structure is only used for transmitting the longitudinal force received by the propeller. Both the upper and lower ends of the force-measuring rod 9 are set as threaded shaft sections. Both ends of the connecting shaft 8 are provided with threaded holes. The upper end is connected to the threaded shaft section of the force-measuring rod 9, and the lower end is connected to the threaded shaft section of the stepped fixed shaft 6. The middle section is fixed with a force-measuring disk 7, which is fixed to the connecting shaft 8 by an interference fit. The disk surface of the force-measuring disk 7 is very thin, and the outer periphery is thickened. The walls are in close contact so that only the radial force along the disk surface is transmitted, i.e., the lateral and vertical dynamic forces acting on the propeller. This decouples the triaxial force measurement sensor embedded in the shaft system. Simultaneously, the thickened portion of the force measuring disk 7 is fixed to the stepped end face of the mounting shaft 3 by four evenly distributed screws. A piezoelectric ceramic plate 11 is fixed on the stepped fixed shaft 6. The piezoelectric ceramic plate 11 comprises three annular piezoelectric ceramic plates, which convert the longitudinal, lateral, and vertical dynamic forces acting on the propeller into electrical signals, respectively. It features high voltage performance, good stability, high-frequency response, and good durability. It is installed on the stepped fixed shaft 6 with a clearance fit and pressed by the lower end face of the adapter shaft 8. The stepped fixed shaft 6 is fixed to the inner end face of the long shaft 5 by threads. Through holes 10 are provided radially and axially on the stepped fixed shaft 6, and through holes 10 are provided axially on the long shaft 5. Circuitry is installed inside the through holes 10.

[0060] Example 2

[0061] The present invention also provides a measurement method for the three-dimensional excitation force measuring device of the piezoelectric decoupled thruster in Embodiment 1, such as... Figure 4-5 As shown, it includes the following steps:

[0062] S1: Install the triaxial piezoelectric force sensor 12. First, mate the force measuring rod 9 with the adapter shaft 8. Then, install the force measuring disk 7 on the adapter shaft 8 with an interference fit. Next, connect all three to the mounting shaft 3 and connect the force measuring disk 7 to the mounting shaft 3 with four evenly distributed screws. This is called assembly a. Then, connect the piezoelectric ceramic plate 11, the stepped fixing shaft 6, and the long shaft 5. This is called assembly b. Finally, assembly a and assembly b are connected through the threaded structure of the adapter shaft 8 and the stepped fixing shaft 6, and the mounting shaft 3 is fastened to the long shaft 5 with bolts.

[0063] S2: The equivalent longitudinal stiffness, equivalent lateral stiffness, and equivalent vertical stiffness of the triaxial piezoelectric force sensor 12 and the combined action of the triaxial piezoelectric force sensor 12 and the hollow tube wall of the transmission shaft are calculated by experiment. The measurement scaling factors of the longitudinal, lateral, and vertical excitation forces are calculated and retained as parameters.

[0064] S3: Controls the propeller to start working, and the propeller is subjected to dynamic excitation force;

[0065] S4: The dynamic excitation force received is converted into a response signal by the triaxial piezoelectric force sensor 12, and the response signal is input into the PC through the LMS data acquisition system;

[0066] S5: The PC processes the input signal according to the measurement scaling factor obtained in step 2, thereby realizing the reconstruction of the dynamic excitation force.

[0067] In step 2, the triaxial piezoelectric force sensor 12 is connected in parallel with the hollow tube wall of the mounting shaft 3 and the long shaft 5.

[0068] like Figure 4 As shown, taking the calculation of the equivalent longitudinal stiffness of the combined action of the triaxial piezoelectric force sensor 12 and the pipe wall as an example, it is equivalent to the hollow shaft thin wall stiffness and the longitudinal stiffness of the triaxial piezoelectric force sensor 12 being connected in parallel. The equivalent longitudinal stiffness of the hollow shaft thin wall is:

[0069]

[0070] Among them, E t Let A be the elastic modulus of drive shaft 1. t Let l be the cross-sectional area of ​​the hollow shaft of drive shaft 1. t The length of the hollow section formed by the blade mounting shaft 3, connecting shaft 13, and long shaft 5.

[0071] The longitudinal equivalent stiffness of the triaxial piezoelectric force sensor 12 was measured to be k through experiments. z Therefore, the total equivalent longitudinal stiffness of the embedded triaxial piezoelectric force sensor 12 and the tube wall is:

[0072]

[0073] And k x With k t The magnitudes are similar, therefore the hollow portion of drive shaft 1 will help distribute the force on the sensor. The longitudinal measurement scaling factor is calculated as follows:

[0074] α x =k1 / k x

[0075] Similarly, the scale factors for lateral and vertical measurements are calculated using α. yWith α z express.

[0076] like Figure 5 As shown, in step 5, the response signal is input into the PC through the LMS data acquisition system. The input signal is processed by measuring the scaling factor. The calculation formulas for the three-dimensional unsteady excitation force are as follows:

[0077] Longitudinal force:

[0078] F x =α x *f x

[0079] Lateral force:

[0080] F y =α y *f y

[0081] Vertical force:

[0082] F z =α z *f z

[0083] Among them, f x f y with f z These are the longitudinal, lateral, and vertical response measurement results of the triaxial piezoelectric force sensor 12, respectively.

[0084] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0085] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A piezoelectrically decoupled thruster three-axis excitation force measurement device, characterized by, The application relates to a three-way piezoelectric force sensor (12), a propeller and a transmission shaft, one end of the three-way piezoelectric force sensor (12) being connected with the propeller, the other end of the three-way piezoelectric force sensor (12) being connected with the transmission shaft, and the three-way piezoelectric force sensor (12) being installed inside the transmission shaft. The three-way piezoelectric force sensor (12) measures unsteady hydrodynamic force or unsteady aerodynamic force of the propeller in longitudinal, transverse and vertical directions. The transmission shaft comprises a mounting shaft (3) and a long shaft (5), the mounting shaft (3) and the long shaft (5) are in clearance fit, and the three-way piezoelectric force sensor (12) is arranged inside a hollow structure formed by the mounting shaft (3) and the long shaft (5). The mounting shaft (3) and the long shaft (5) are in hollow structure, the lower end surface of the hollow structure of the mounting shaft (3) is in stepped shaft structure, the upper end surface of the hollow structure of the long shaft (5) is in stepped shaft structure, the lower end surface of the mounting shaft (3) and the upper end surface of the long shaft (5) are in clearance fit through the stepped shaft structure, and the mounting shaft (3) and the long shaft (5) are fixedly connected through bolts. The three-way piezoelectric force sensor (12) comprises a stepped fixed shaft (6), a force measuring disc (7), an adapter shaft (8) and a force measuring rod (9), one end of the adapter shaft (8) is connected with the force measuring rod (9), the other end of the adapter shaft (8) is connected with the stepped fixed shaft (6), and the force measuring disc (7) is fixedly arranged in the middle end of the adapter shaft (8) in interference fit. The force measuring disc (7) is in contact with the inner wall of the mounting shaft (3), the force measuring disc (7) transmits force along the radial direction of the disc surface, and the three-way piezoelectric force sensor (12) is decoupled. The middle part of the force measuring rod (9) is in thin rod structure, the force measuring rod (9) transmits longitudinal force received by the propeller through the thin rod structure.

2. The piezoelectrically decoupled thruster three-axial excitation force measurement device of claim 1, wherein, The upper end and the lower end of the force measuring rod (9) are provided with threaded shaft sections, the upper end of the force measuring rod (9) is fixedly connected with the inner end surface of the mounting shaft (3) through a threaded structure, and the lower end of the force measuring rod (9) is connected with the upper end of the adapter shaft (8) through a threaded structure. The thickened part of the periphery of the force measuring disc (7) is fixed on the stepped end surface of the mounting shaft (3) through uniformly distributed screws.

3. The piezoelectrically decoupled thruster three-axis excitation force measurement device of claim 1, wherein, A plurality of piezoelectric ceramic sheets (11) are arranged in clearance fit on the stepped fixed shaft (6), the stepped fixed shaft (6) is pressed through the lower end surface of the adapter shaft (8), and the piezoelectric ceramic sheets (11) are fixedly connected with the inner end surface of the long shaft (5) through threads.

4. The piezoelectrically decoupled thruster three-axis excitation force measurement device of claim 1, wherein, The piezoelectric ceramic sheets (11) are in ring shape, and the plurality of piezoelectric ceramic sheets (11) respectively convert longitudinal dynamic force, transverse dynamic force and vertical dynamic force received by the propeller into electric signals. The propeller comprises a propeller hub (1), a propeller blade (2) and a propeller hub cap (4), the propeller hub (1) is fixed with the propeller blade (2), the propeller hub (1) is arranged on the mounting shaft (3) through a threaded structure, and the propeller hub (1) is fixed through the propeller hub cap (4).

5. The piezoelectrically decoupled thruster three- directional excitation force measurement device of claim 1, wherein, The application further discloses a three-way piezoelectric force sensor (12) measurement method.

6. A measuring method of a three-directional exciting force measuring device for a piezoelectric decoupled thruster according to any one of claims 1 to 5, characterized by, ​ S1: install the three-way piezoelectric force sensor (12), first, the force bar (9) is matched with the adapter shaft (8), the force disc (7) is installed on the adapter shaft (8) through interference fit, then the three are fixed with the mounting shaft (3), and the force disc (7) is connected with the mounting shaft (3) by four evenly distributed screws, which is marked as assembly a; The piezoelectric ceramic sheet (11) and the stepped fixed shaft (6) are fixed with the long shaft (5), which is marked as assembly b; Finally, the assembly a and the assembly b are matched through the threaded structure of the adapter shaft (8) and the stepped fixed shaft (6), and the mounting shaft (3) and the long shaft (5) are fastened by bolts; S2: the equivalent longitudinal stiffness, the equivalent transverse stiffness and the equivalent vertical stiffness of the three-way piezoelectric force sensor (12) and the comprehensive action of the three-way piezoelectric force sensor (12) and the hollow structure pipe wall of the transmission shaft are calculated, and the measurement proportional factor of longitudinal, transverse and vertical excitation force is calculated as a parameter; S3: control the propeller to start working, and the propeller is subjected to dynamic excitation force; S4: the dynamic excitation force received by the three-way piezoelectric force sensor (12) is converted into a response signal, and the response signal is input into a PC through an LMS data acquisition system; S5: the PC processes the input signal according to the measurement proportional factor obtained in step S2, so as to realize the reconstruction of the dynamic excitation force.

7. The method of measuring a piezoelectrically decoupled thruster three- dimensional excitation force measurement device according to claim 6, characterized in that, In step S2, the three-way piezoelectric force sensor (12) is connected in parallel with the mounting shaft (3) and the long shaft (5) hollow structure pipe wall; The equivalent longitudinal stiffness of the three-way piezoelectric force sensor (12) and the pipe wall comprehensive action is calculated, which is equivalent to the parallel connection of the longitudinal stiffness of the three-way piezoelectric force sensor (12) and the longitudinal equivalent stiffness of the hollow shaft thin wall, and the longitudinal equivalent stiffness of the hollow shaft thin wall is: wherein, E is the modulus of elasticity of the transmission shaft, A is the cross-sectional area of the hollow shaft of the transmission shaft, L is the length of the hollow portion formed by the mounting shaft (3), the adapter shaft (8) and the long shaft (5). The longitudinal equivalent stiffness of the three-way piezoelectric force sensor (12) is K x , so the total equivalent longitudinal stiffness of the embedded three-way piezoelectric force sensor (12) and the pipe wall is: And With The hollow part of the transmission shaft shares the force of the three-way piezoelectric force sensor (12); the longitudinal measurement scale factor is calculated as: The lateral and vertical measurement scale factors are calculated in the same way and are denoted by and respectively.

8. The method of measuring a piezoelectrically decoupled thruster three- dimensional excitation force measurement apparatus according to claim 6, characterized by, In step S5, the response signal is input into the PC through the LMS data acquisition system, and the input signal is processed through the measurement proportional factor, and the calculation formula of the three-way non-steady excitation force is respectively: Longitudinal force: Transverse force: Vertical force: wherein, , with are the longitudinal, transversal and vertical response measurements of the tri-axial piezoelectric force sensor (12), respectively.

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