A lot of people use electromagnetic brakes and clutches on daily basis without really realizing it. Anyone who switches on a copy machine, car air con or a lawn tractor may be using an electromagnetic clutch (the brakes are just as common) which operates electrically but transfers torque mechanically. You might find both EM clutches and brakes in many forms, including multiple disc, tooth, magnetic particle and hysteresis, but the most commonly known version is the single-face EM design.
Both EM brakes and clutches fall under the same electromagnetic braking system, which is comprised of the following structural components: a field (coil in a shell), a hug and an armature. Clutches also consist of a rotor which is connected to the driveshaft. The field is typically carbon steel, which combines magnetic properties and strength. The coil is typically made of a copper wire or aluminium, and an epoxy or bobbin adhesive holds the coil in the shell.
By activating the electric circuit of the electromagnetic braking system, you energize the coil, which then runs through the coil and generates a magnetic field. Then the air gap between the field and the armature is overcomed by the magnetic flux, it causes the magnet to pull the armature, which then connects to the hub and the rotor.
Since brakes don’t have a rotor, the magnetic flux acts directly between the field and armature. The field is usually bolted to the frame of the machine or on a torque arm which handles brake torque. When the field comes in contact with the armature, the braking torque transmits into the machine frame and field housing, decelerating the load.
For most industrial applications, a single-flux, twopole clutches are ideal. These have a single north-south flux path between the armature and rotor. However, specialty EM clutches can use a double or even triple-flux rotor. These clutches have more slots in both the armature and rotor which create extra air gaps between both parts. These slots run parallel to the armature or rotor circumference, so they’re often known as banana slots.
The ability to increase torque without a larger of heavier clutch is of utmost importance in weight-sensitive applications. When you turn off the power in both brakes and clutches, the coil will disengage the unit. As soon as the power is down, the flux will fall rapidly and the armature will separate. A single or multiple springs help maintain a predetermined air gap and push the armature away from the contact surface.