e produced by the vibrator is the longitudinal force, forcing the sieve box to drive the screen surface as the longitudinal front and back displacement. Under certain conditions, the material on the screen surface is thrown forward by the excitation force and is less than the sieve hole when it falls. The material is sifting and falling to the lower layer. The movement of the material on the screen surface is parabolic movement. As the material moves from the end of the material into the sieve b