Electromagnetic Brakes: Past Innovations, Present Functions

Electromagnetic brakes come in various forms (tooth, multiple disc, hysteresis, magnetic particle). The variant with a single-face design is the most popular. While mechanically transmitting torque, electromagnetic brakes function electrically. They were once known as electromechanical clutches and brakes for this reason. The range of applications and brake designs has expanded significantly since electromagnetic brakes gained popularity over seventy years ago, but the fundamental workings of the single-face electromagnetic brake have not changed.



Consider the coil shell as a north and south-pole horseshoe magnet. A magnetic circuit is formed if a piece of iron makes contact with both poles. An electric field is produced when power is provided, and this field (flux) bridges the gap between the armature and the field. The armature is drawn into contact with the brake field face by this magnetic attraction. The circular motion comes to an end due to friction and the intensity of the magnetic field. The magnetic attraction and coefficient of friction between the armature's steel and the rotor's or brake field's steel account for nearly all of the torque. However, friction material is employed between the poles of many industrial clutches and brakes. The primary purpose of the material is to aid in lowering the wear rate. However, for certain uses, the coefficient of friction may also be altered with different kinds of material. Low coefficient materials, for instance, can be utilised if the brake is required to have a prolonged slip time or time to stop. Conversely, a high coefficient of friction material may be chosen if a somewhat larger torque was needed from the brake.

The coil is made of copper (or occasionally aluminium) magnet wire and is secured within the shell using epoxy or glue and a bobbin. The friction material is then positioned over the coil and between the inner and outer poles of most industrial brakes. 

Function

The field, armature, and hub—which serves as the brake's input—are the only three major components of a brake. Typically, the magnetic field has a torque arm or is fastened to a solid surface. Consequently, the stopping torque is transmitted into the field housing when the armature is drawn to the field, slowing down the load. This can occur quickly. However, the amount of voltage or current provided to the field can determine the braking time to stop.

As soon as the field begins to weaken, the armature separates and flux drops off quickly. The armature is kept at a preset air gap from its field face surface by one or more springs.


Location: Hayes Ln, Stourbridge DY9 8QT, UK

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