Brakes and Clutches
Hysteresis Principles

Principles of Hysteresis

Cross section

Operating Principles

The hysteresis effect in magnetism is applied to torque control by the use of two basic components–a reticulated pole structure and a specialty steel rotor/shaft assembly–fastened together but not in physical contact. Until the field coil is energized, the drag cup and shaft can spin freely on its bearings. When a magnetizing force from either a field coil or magnet is applied to the pole structure, the air gap becomes a flux field. The rotor is magnetically restrained, providing a braking action between the pole structure and rotor. Because torque is produced strictly through a magnetic air gap, without the use of friction or shear forces, Hysteresis Brakes provide operating characteristics such as:
  • Absolute Smoothness
  • Torque Independent of Speed
  • Total Adjustability
  • Long, Maintenance-Free Life
  • Highest Degree of Repeatability
  • Quiet Operation
  • Stability
In an electrically operated Hysteresis Brake, adjustment and control of torque is provided by a field coil. This allows for complete control of torque by adjusting DC current to the field coil. Adjustability from a minimum value (bearing drag) to a maximum value of rated torque is possible. Additional torque in the range of 15-25% above rated torque may be available on some brakes.

The amount of braking torque transmitted by the brake is proportional to the amount of current flowing through the brake coil. The direction of current flow (polarity) is of no consequence to the operation of the brake. For optimum torque stability, a DC supply with current regulation is recommended. This will help to minimize torque drift attributable to changes in coil temperature and in-line voltage, which can result in changes in coil current, and consequently, in torque.
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