Depending upon the mounting method, these units can function as either a clutch or a brake. Torque is generated magnetically, but is a function of the unit's mechanical setting. Each unit has an individual torque range. Once that torque is set, torque is generally stable, regardless of speed (within the unit's speed range). This makes these units ideally suited for tension control applications. Paper, film, foil, wire and other material tensions can be easily controlled. Since these units do not require a power supply, they are very cost effective. Typical applications include motor test stands, small wire winding, bottle cap machinery and labeling equipment. Since the units are sealed and do not develop wear particles, they are also adaptable to medical equipment and office automation machinery that requires control for paper tension. (Office automation versions of these units are extremely cost effective.)
No electrical power needed: The permanent magnet hysteresis units do not require any external power, which means their function is independent from power fluctuations.
No contamination: Since there are no wearing parts, and the units are sealed, there are no wear particles from these units that can contaminate your machine.
Stable torque: A consistent torque is maintained, regardless of allowable slip speed, due to the hysteresis principle.
Minimal stick slip: Since torque is transmitted magnetically, there is no friction from which to break away. This means that static and dynamic torques are almost the same.
How It Works
Function: Most units contain a hysteresis disk, which is directly attached to the hub that passes through the clutch/brake. Two circular multiple pole magnets are solidly attached internally within the unit. The magnets face each other with the hysteresis disk between them. There is an air gap between the magnets and the hysteresis disk, so the hysteresis disk can turn without any frictional contact. The opposing circular magnets set up magnetic flux, which causes drag on the hysteresis disk, which in turn, causes drag to the hollow hub in the unit.
To increase or decrease the amount of output drag, the units are manually adjustable. As the magnet poles are aligned north to south with each other, they produce the maximum amount of drag on the hysteresis disk. As the poles are changed from a north to south alignment, the flux passes directly through the hysteresis material, reducing the amount of drag on the hollow hub of the unit.