| With small multi-rotor UAVs(Unmanned Aerial Vehicle) being more and more widely used, vibration analysis and vibration study has become a key technology in further development of multi-rotor UAV. In this essay, based on the structural characteristics of self-developed Hex-rotor UAV, vibration design of its inertial sensor unit is conducted. The design process starts from analysis of vibration with the usage of signal processing knowledge. The multi-rotor UAV vibration measurement is conducted and its characteristics are summarized. According to the theory of damping, a damping structure is designed with finite element method. And finally the rationality of damping structure is validated by the simulation experiment, measurement experiments and practical work performance. The main contents of this essay include:(1) Analysis of Hex-rotor structural characteristics of multi-rotor UAV and the role UAV’s sensor in control. Sum up the characteristics inertial measurement unit and the impact of vibration on the attitude angle. Thereby emphasize importance of the design goal while providing ideas for damping effect assessment. Make modifications on in the existing multi-rotor UAV control system’s hardware and program, and a build multi-rotor UAV vibration signal speed feedback system which can achieve high-speed three-axis acceleration signal return in real-time. The return signal frequencies is above 250 Hz. Using this system, an acceleration measurement experiments was designed considering the environment and disturbance features of the multi-rotor UAV.(2) Collect three-axis acceleration signal data under motor speed of about 2400 r/ min and 3600r/min separately. Considering the installation of the inertial measurement units, Z-direction is chosen for further research. First, time domain characteristic of the measured acceleration signal is analyzed. Then transfer the signal into the frequency domain using Fourier transform. Frequency domain analysis shows that large amplitude can be found on the multiples of the current motor frequency. Finally, conclude a general multi-rotor UAV vibration spectrum model and analyze the causes of the vibration frequency components.(3) Vibration design using finite element analysis software ANSYS. First, conduct modal analysis for the recommended mounting structure of the inertial measurement unit, and prove that the strength of the structure is sufficient. Then based on vibration knowledge and characteristics of rubber materials, a reasonable damping structure was designed. Finite element method is later used to analyze structural vibration frequency response characteristics.(4) Authentication of the damping structure. First estimate the relationship between acceleration and angular error when the UAV is in the vicinity of the horizontal position. Then based on the principle of Kalman filtering, establish a gyroscope and accelerometer sensor data fusion model. Choose the appropriate parameters and run the simulation in Matlab. Results indicate that vibration error and the angular error after fusion is decrease at the same time. After that, the designed damping structure is mounted onto the multi-rotor UAV, and the acceleration is measured again for comparison. Finally, evaluate the effect of the damping design through multi-rotor UAV’s practical flight.Since the multi-rotor UAV itself is a complex electromechanical systems, vibration research involves signal processing, electronics, mechanical design and control theories, etc. Although relatively basic, the content of this article covers all these areas. The basic elements of a complete multi-rotor UAV vibration design considerations are listed, and the design process and methods have certain reference value for related research. The designed damping structure is adapted on the Hex-rotor UAV and achieved good results in practical use. |
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