Abstract
<jats:p>Abstract The article presents the results of a study aimed at substantiating the working height of a brush cutter rotor. To describe the branch response, a model based on the Euler–Bernoulli equations with the projection of the impulse force onto modal forms was used, which describes the energy distribution and maximum displacements depending on the impulse, impact duration, branch geometry, and the point of application x_0. Analytical expressions for natural frequencies and vibration modes, formulas for calculating the modal energy and the dependence of the oscillation energy and branch deviation on the impact impulse and the height of its application to the branch were obtained. These formulas make it possible to relate the rotor parameters - rotation frequency, mass, blade distance from the rotor axis - with the expected oscillations and branch fracture. For a branch 1.5 m long and 0.01 m in diameter, the obtained natural frequencies of the first five vibration modes were 2.91; 17.34; 48.25; 94.51 and 156.17 Hz. To verify the modal analysis, a frequency analysis was performed in CAD; the deviation of natural frequencies for the first five modes is less than 1%. A model of the rotor hydraulic drive was developed, taking into account its inertial parameters and pressure changes in the pressure hydraulic line. It was found that when cutting branches with a diameter of 10…30 mm, the energy from the flywheel inertia is primarily consumed, which is restored by the drive between blows. The obtained theoretical values during branch cutting are compared with the results of experimental studies on a prototype brushcutter rotor. It was found that the hydraulic drive model satisfactorily describes the pressure changes in the hydraulic system. The most rational cutting height is shown to be 0.2…0.4 m. The obtained results can be used in the design of brushcutters and the selection of the parameters of their working tools. Limitations of the model: linearization, the need for calibration of parameters for different wood species.</jats:p>