Test and analysis of vibration characteristics of transplanting machine based on time frequency and power spectral density

A large-amplitude vibration commonly occurs in most agricultural machinery at present in China. The resulting high failure rate and low reliability have posed great damage to the structural safety and driver comfort of the machine. Many efforts have been made on the vibration modes and testing in agricultural harvesting machines. But only a few focused on the vibration of planters, especially a high-speed transplanting machine. Most previous tests show that the variable speed rotation or swing of the mechanism can significantly cause the impact vibration and inertia force of components, particularly with the increase of picking speed. As such, there is a huge decline in the success rate of picking seedlings, while leading to a high missing rate of seedlings, due mainly to the operational instability and high errors. However, no good solutions were reported to deal with that so far. In this study, taking a top clamp-type pneumatic transplanter (2ZZT-2) of vegetable as the research object, the vibration characteristics of a transplanter was investigated using the time-frequency analysis. A dynamic signal instrument (DH5902) and 3-way acceleration sensor (356A16 type) were first used for the data acquisition. A time-frequency analysis was performed on the MATLAB software, where the power spectral density was adopted to analyze the vibration data. The distribution characteristics of signal energy were obtained on the time- and frequency-axis. Secondly, the local resonance was also verified for the test components. The hammering and multi-point excitation were utilized to determine the response of hammering excitation and vibration data in the measuring points of components. Correspondingly, a specific relationship was obtained between the frequency of each measuring point and the first five natural frequencies. The experimental results showed that the main sources of vibration in the transplanter were derived from the swing of the mechanical arm and the transverse movement of the seedling plate. The secondary sources of vibration were the opening and closing of the seedling picking manipulator, and the stretching of the top seedling mechanism in the whole machine. The energy intensity of vibration was distributed mainly at the low frequency (0-10 Hz) during the transplanting operation. The amplitude was 5.43 m/s2, when the seedling manipulator swung, and 1.71 m/s2 when the whole machine working, indicating the amplitude decreased by 68.51% than before. In addition, the vibration frequency (6.10 Hz) caused by the swinging of the seedling taking manipulator was close to the fifth natural frequency (6.25 Hz) at the measuring point, when the transplanter was working normally, indicating the resonance occurred. The finding can provide a sound reference to improve the vibration performance for the high reliability of a transplanter.