There are a number of types of mechanical screening equipment that cause segregation. These types are based on the motion of the machine through its motor drive.
*Circle-throw vibrating equipment -  This type of equipment has an eccentric shaft that causes the frame of the shaker to lurch at a given angle.  This lurching action literally throws the material forward and up.  As the machine returns to its base state the material falls by gravity to physically lower level. This type of screening is used also in mining operations for large material with sizes that range from six inches to +20 mesh.
*High frequency vibrating equipment -  This type of equipment drives the screen cloth only.  Unlike above the frame of the equipment is fixed and only the screen vibrates.  However, this equipment is similar to the above such that it still throws material off of it and allows the particles to cascade down the screen cloth. These screens are for sizes smaller than 1/8 of an inch to +150 mesh.
*Gyratory equipment -  This type of equipment differs from the above two such that the machine gyrates in a circular motion at a near level plane at low angles.  The drive is an eccentric gear box or eccentric weights.  
*Trommel screens - Does not require vibration.  Instead, material is fed into a horizontal rotating drum with screen panels around the diameter of the drum.