Cottonseed particle motion Law in 3-DOF hybrid vibration screen surface

Abstract: To further study and reveal material movement rule and penetrating screening mechanism on multidimensional vibrating screen as well as to design a hybrid vibrating screen of three degrees of freedom (3-DOF), the paper, based on topological structure theory in mechanism, has constructed a complete decoupling 3-DOF hybrid organization of 2PRRR－P(2R) as the main body of vibration mechanism in the 3-DOF hybrid vibrating screen and has designed an experiment prototype of the 3-DOF hybrid vibrating screen. The simulation test of screen movement on the screen surface was carried out and analyzed. Cotton seed particles of ellipsoid were taken as the typical materials. Movement rule of material particle group on the screen surface of the 3-DOF hybrid vibrating screen was analyzed. D-H transformation matrix was used to deduce motion trace equation on the screen surface. The kinematics simulation was carried out with ADAMS software, and the feasibility of the mechanism design has been verified. Based on the discrete element method, the paper used optimal selection of difficult ellipsoid cotton seed particles of ellipsoid that is difficult in screening in agricultural materials as the screening objects, and carried out simulation analysis on screening process of cotton seed particle group on the screen surface of the 3-DOF hybrid vibrating screen. In the simulation test, optimal screen size is 280 mm × 160 mm and contact model between cotton seeds and screen surface belongs to the Hertz model. Set in the rectangle form of 140 mm × 80 mm, particle factory produced 10 000 cotton seed particles and particle generation rate was 5, 000 per second. The simulation time was 8 s. In the experiment, reciprocating motions in Z, XZ and XYZ directions were respectively added on the screen surface. Based on truncation technique, the average values of three-coordinate in borderless particles collision were respectively extracted and the particle group displacement time curve on the screen surface was drawn. Simulation test results showed that when the screen surface vibrated in XYZ direction, three-direction displacement curve of cotton seeds displayed periodicity and the X and Y directions showed the larger throwing displacement. After 3.6 s, particles penetrating screening completed. When the screen surface vibrated in Z direction only, there was a small amount of displacement fluctuation in cotton seed particles in the X and Y directions. After 6.4 s of particles' penetrating screening, the average penetrating screening time increased by 77% compared with vibrating particles group on the screen surface in XYZ direction. When the screen surface vibrated in XZ direction, cotton seeds particles in X direction had the relatively great throwing displacement. After 5.1 s, particles' penetrating screening completed. The average penetrating screening time was shortened to 38% compared with particles group on screen surface in Z direction only. Average penetrating screening time increased by 43% compared with particles group vibration in XYZ direction on the screen surface. Simulation test results showed that the increase of freedom movement on the screen surface in X and Y directions could increase the particles group's throwing displacement in X and Y directions correspondingly, which was conducive to dispersing particles group on the screen surface, reducing average particles' penetrating screening time and improving the screening efficiency. The dispersion and efficiency of cottonseed particles on three translations of 3-DOF vibration screen surface was verified by testing in the multi-dimensional vibration screening test stand, and the test results were in agreement with the simulation. Research showed that 3-DOF hybrid vibrating screen could realize three-dimensional independent vibration along the X, Y and Z directions. The vibration parameters such as degrees of freedom of vibration, amplitude, frequency could be adjusted conveniently; 3-DOF vibration on the screen surface was conducive to dispersing particles materials on the screen surface and could significantly improve the screening efficiency. The paper provides the reference for further study on the multidimensional vibration principle and for prototype development of 3-DOF hybrid vibrating screen.