|Electromagnetic clutches operate electrically but transmit torque
mechanically, that is why they have also been known as electromechanical
Now we simply call them EM clutches. Electromagnetic clutches that use magnetic particles to cause drag between the input and output are also known as magnetic particle clutches.
Magnetic particle clutches:
Magnetic particle clutches are unique in their design, from other electro-mechanical clutches because of the wide operating torque range available. Like a standard, single face clutch, torque to voltage is almost linear. However, in a magnetic particle clutch torque can be controlled very accurately. This makes these units ideally suited for tension control applications, such as wire winding, foil, film, and tape tension control. Because of their fast response, they can also be used in high cycle application, such as card readers, sorting machines, and labeling equipment. The most common magnetic powders used in EM clutches are IRON325 iron powder and S1001 Steel Powder. IRON325 allows high precision control of torque, smooth operation, low noise. IRON325 particles do not have sharp edges that can cause internal erosion of EM devices.
This is how EM particle clutches work:
Magnetic particles (very similar to iron filings) are located in the powder cavity. Without any voltage/current they sit in the cavity. However, when voltage/current is applied to the coil, the magnetic flux that is created tries to bind the particles together, almost like a magnetic particle slush. As the voltage/current is increased, the magnetic field builds, strengthening the binding of the particles. The clutch rotor passes through the bound particles, causing drag between the input and the output during rotation. Depending upon the output torque requirement, the output and input may lock at 100% transfer.
When voltage/current is removed from the clutch, the input is free to turn with the shaft. Since the magnetic particle is in the cavity, all magnetic particle units have some type of minimum drag associated with them.