Hysteresis brake
A hysteresis brake is a brake that is based on the action of a magnet or electromagnet on a moving, ferromagnetic material. The energy loss is caused by the repeated magnetization of the material.
Layout and function
Hysteresis brakes use a disk attached to the shaft to be braked, a ring or a bell shape made of a ferromagnetic , hard magnetic material (iron alloy) that runs freely with an air gap between alternating magnetic poles. The magnetic field is applied by permanent magnets or a coil through which direct current flows and is accordingly fixed or variable. It leads to a braking torque that is almost proportional to the coil current. Hysteresis clutches can be built according to the same principle .
Magnetic brakes and clutches excited by permanent magnets can also be adjusted with regard to torque by adjusting the pole rings against each other. Poles facing each other result in the smallest moment, but if the south and north poles alternate along the circumference, the strongest magnetic reversal takes place and the moment is greatest.
In contrast to the eddy current brake , the force / torque generated with the hysteresis brake is not dependent on the speed or revolutions per minute; H. the hysteresis brake works evenly from standstill up to the constructively possible maximum speed or speed. The torque-excitation current curve shows a hysteresis curve, that is, the torque is slightly larger or smaller, depending on whether the excitation current has previously increased or decreased.
In the event of a longer standstill, a weak detent torque can form which must be overcome when starting up. This detent torque disappears again due to the function-related magnetization reversal during operation.
Hysteresis brakes are characterized by a long service life, which is only limited by the shaft bearings, due to the non-contact mode of operation and the associated freedom from wear.
Individual evidence
- ↑ a b https://www.magtrol.com/germany/wp-content/uploads/hb_manual_de.pdf Operating instructions Magtrol hysteresis brakes and clutches , page 4f, accessed on March 22, 2018