This type of equipment has an eccentric drive or weights that causes the shaker to travel in an orbital path.  The material rolls over the screen and falls with the induction of gravity and directional shifts.  Rubber balls and trays provide an additional mechanical means to cause the material to fall through.  The balls also provide a throwing action for the material to find an open slot to fall through.
The shaker is set a shallow angle relative to the horizontal level plane.  Usually, no more than 2 to 5 degrees relative to the horizontal level plane.
These types of shakers are used for very clean cuts.  Generally, a final material cut will not contain any oversize or any fines contamination.
These shakers are designed for the highest attainable quality at the cost of a reduced feed rate.