Brake motors are used in applications where stopping must be achieved within a limited duration of time, such as elevators conveyors, cranes, and in operations involving lifting of heavy duty loads. Brake motors are simply standard motors that have been modified to achieve braking. They are therefore 3 phase induction motors with standard output rating and dimensions, but to which brake units have been added. The electromagnetic disc brakes are powered using either alternating current or direct current. The AC current, if used, must be three-phase, and is supplied by a rectifier within the terminal box. The brake units are attached to the motor’s non-drive side and function as electrically-released units, which enables them to provide fail-to-safe operations. In the event that power supply fails or becomes interrupted, the brakes automatically engage, thereby arresting the load.
The method of operation of brake motors is simple. Usually, these motors have a friction disc positioned between two metal plates. While one of them is fixed, the other is designed to allow it to achieve axial movements depending on the direction of the spring pressure. Switching on of the power supply energizes a magnet which in turn compresses the spring forcing it to exert no pressure on the plates. In such a condition, the motor shaft is free to rotate. When the supply is cut off, the brake becomes de-energized and the pressure from the spring acts on the metal plates, which in turn act on the friction disk.
There are different braking modes. The choice of any particular mode is influenced by the braking requirements as well as the application. Therefore, a person seeking to acquire a brake motor should give all the details pertaining to the braking mode, to ensure that the motor selected meets the desired performance. Some of the most common modes of breaking include holding, overhauling breaking, load-assisted braking, and soft-stop breaking.
Brook Crompton. (2010). Brake motors: from 63 to 355L range. Retrieved from http://www.brookcrompton.com/upload/files/products/2010e_brakes_v1.pdf