Rotary solenoids are electromechanical devices that convert axial motion into rotary strokes. These transducers have a higher starting force (torque) than linear solenoids, and are more resistant to shock. Actuators that are mounted on the opposite ends of a shaft or plunger provide a ratcheting action and advance or reverse position. 

 

Many rotary solenoids include small ball bearings that ride on an inclined plane. Electrical current is supplied to a coil wound tightly enough to limit the current drain and sized large enough to provide for adequate heat dissipation. The resulting magnetic field draws the plunger from its unpowered, extended position to a seated position against a backstop or pole piece. Because the linear force on the plunger is nonlinear with position, the force is relatively high immediately adjacent to the seated position and declines rapidly with increased distance from the seated position.

 

Typically, rotary solenoids are used where space is limited and when long life is required (e.g., laser shutters). Their energized rotation (direction) is characterized as either clockwise or counterclockwise when viewed from the armature flange end. Most products have a spring return to bring the armature back to the home position when power is removed.

 

Types of Rotary Solenoids

The GlobalSpec SpecSearch database contains information about these types of rotary solenoids.

  • Bi-stable rotary solenoids can be driven in either direction (clockwise or counterclockwise) and remain in either end-position  without the continuous application of power. They have fast response times and are often used in document movement and sorting systems.  
  • Step rotary solenoids have additional magnetic poles for multiple position control. These durable, high-torque devices are similar to bi-stable products in that a permanent magnet holds the position even when power is not applied.
  • Latching solenoids also use permanent magnets to maintain position. They are designed for low duty cycle applications such as door locks where the energized position must be maintained for an extended period of time. The application of a negative electrical pulse unlatches the plunger.

Rotary solenoids are also classified based upon their suitability for continuous or intermittent duty. Intermittent duty solenoids are considerably smaller than continuous duty devices, and provide less pull-and-hold strength.

 

Performance Specifications

When selecting rotary solenoids, buyers should consider application requirements such as maximum rotary stroke, axial stroke, and response time. The maximum rotary stroke is the full rotary travel in angular units. The axial stroke is the axial travel of the solenoid during actuation, as measured in units of distance. Response time is the time required to move full-stroke under no-load conditions.

 

References

 

Solenoid Basics

 

Solenoid Glossary