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Hysteresis clutches transmit torque between two rotating shafts through the magnetic hysteresis of a steel disc — no friction surfaces, no physical contact between the input and output members. When DC current is applied to the coil, a magnetic flux field is established across the hysteresis disc. The drag force between the disc and the magnetic field generates torque between the shafts. Torque is directly proportional to coil current, independent of slip speed, and smooth across the full RPM range. When current is removed, the flux dissipates and the shafts rotate freely relative to each other.
Because no parts contact each other during torque transmission, there are no friction surfaces to wear. Torque output under identical current conditions is repeatable over the full service life of the unit. This makes hysteresis clutches the correct choice for applications where torque consistency and repeatability matter more than torque magnitude — light tension control on fine wire and filament, small precision assemblies, lab instruments, and test and measurement equipment.
The Ogura HC series covers a torque range of 0.0367 to 0.741 ft-lbs (0.44 to 8.9 in-lbs) at 24 VDC, with bore sizes from 5 to 10 mm and a maximum RPM of 3,000. This is a light-duty precision unit. For higher torque hysteresis braking applications, the Ogura HB series hysteresis brake covers 0.12 to 1 Nm on the brake side.
A hysteresis clutch generates torque between two rotating shafts by establishing a magnetic flux field across a steel hysteresis disc. The interaction between the rotating disc and the stationary flux field creates a drag torque that is transmitted between the shafts without physical contact. Torque is proportional to coil current and independent of slip speed. When current is removed, the flux dissipates and the shafts rotate freely relative to each other.
What is the difference between a hysteresis clutch and a magnetic particle clutch?
Both transmit torque without friction contact and both have torque proportional to current. The key difference is the torque transmission mechanism. A hysteresis clutch uses the magnetic properties of a steel disc — no particles, no wear material, and no contamination risk. A magnetic particle clutch uses powder particles to form chains between input and output members. Hysteresis clutches produce smoother, more consistent torque at very low levels. Magnetic particle clutches cover a wider torque range and faster torque response. For very light precision tension applications, the hysteresis clutch is generally the more appropriate choice.
What applications use electromagnetic hysteresis clutches?
Hysteresis clutches are used in light tension control for fine wire, filament, thread, and thin film processing; test and measurement equipment requiring repeatable known torque loads; lab instruments and precision assemblies; small automation systems; and calibration equipment. The HC series torque range of 0.0367 to 0.741 ft-lbs targets light-duty precision applications — not high-torque industrial machinery.
Does hysteresis clutch torque change as the unit ages?
No. Because torque is generated magnetically with no friction surfaces in contact, there is no wear that would change the torque output over time. Under identical current conditions, the HC series will duplicate its torque performance throughout its service life. The only wearing components are the bearings.
What is the difference between the Ogura HC hysteresis clutch and the HB hysteresis brake?
The HC is a clutch — both the input and output members rotate, and the unit controls the torque transmitted between two rotating shafts during continuous slip. The HB is a brake — one member is stationary and the unit resists or stops rotation of the moving shaft. Both use the same hysteresis operating principle. The HC covers 0.0367 to 0.741 ft-lbs at 24 VDC. The HB covers 0.12 to 1 Nm at 24 VDC. Selection depends on whether the application requires torque control between two rotating shafts or braking torque against a fixed structure.
Can hysteresis clutch torque be adjusted during operation?
Yes. Torque is directly proportional to coil current. Varying the current during operation adjusts the transmitted torque in real time without affecting shaft speed or requiring mechanical adjustment. Once current is held stable, torque remains constant regardless of the slip speed between the shafts.
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