The frame of screen 2 is suspended from the upright by identical parallel suspension links 4. The frame of screen 3 is suspended from the upright by identical parallel suspension links 5. Screens 2 and 3 have lugs a. Springs 6 are arranged between lugs a and fixed frames b. Vibratory motion is imparted to the mechanism by rocker arm 1, oscillating about fixed axis A and actuating springs 7 which are connected to the frames of screens 2 and 3. When rocker arm 1 oscillates, screens 2 and 3 have vibratory motions.
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