Counting the shake in g
Screen builders rate shaking by peak acceleration compared with gravity. For simple harmonic motion the peak acceleration is the angular frequency squared times the amplitude, so g-force = (2 pi f) squared times amplitude, divided by 9.81. Many inclined screens run somewhere around 3 to 5 g; treat that band as a rule of thumb, not a design value.
Doubling the frequency multiplies the g-force by four, while doubling the amplitude only doubles it. That is why fine screens often run fast with short strokes and coarse screens run slower with long strokes.
Try it: set 25 Hz and 6 mm. The g-force passes 15, far beyond a normal screen. Now drop to 14 Hz and 4 mm to get back near 3 g.
Simplified motion
The scene shows only the up and down part of the motion, slowed down a lot. Real inclined screens move in a circle or ellipse, which also pushes the bed along the deck.