Small Rotary Solenoids in Shutter Applications:
A Technical Overview
Bistable Rotary Solenoids in Shutter Applications
Bistable Rotary Solenoids
Geeplus offers small bistable rotary solenoids and actuators in several types, suited to actuation of small shutter mechanisms. These typically require rotation of a small ‘flag’ to block or pass a light beam, or of a small mirror to deflect a light beam down another path.
What Applications does this Suit?
These miniature rotary solenoids / actuators are suited to small shutter mechanisms where the mass of moving elements is low, and is balanced about the axis of rotation. Fast actuation (<2ms) is possible for small angles and loads. Check out the video below to see an example of this with the BRS1212 Bistable Rotary Solenoid (content continues below video):
What Differentiates this from Other Solutions?
These rotary solenoid devices are brushless with a fixed coil and moving magnet rotor. Therefore the solenoids do not exhibit the wear and reliability concerns associated with brushed motors. These actuators can endure high pulse currents without damage, for high torque / fast operation.
Bistable rotary solenoid operation allows the device to be driven from open to closed position, or vice versa, with a short excitation pulse. The solenoid will then hold this end position without power being applied.
• This reduces the power consumption in battery-powered systems.
• In applications such as thermal imaging, the reduction of heat dissipation from the bistable rotary solenoid reduces disturbance of the sensors in the imaging system.
• If ‘fail-safe’ operation is required where the rotary solenoid must return to a known state in the event of power failure, bistable operation may not be appropriate
By balancing the moving elements about the axis of rotation, the rotary solenoid mechanism can be made highly resistant to shock applied in a linear direction, and friction can be minimised with inexpensive bearings.
DESIGN (Bistable Rotary Solenoid)
The most widely used rotary actuators are moving magnet galvanometers or bistable rotary solenoids. The typical construction of these is shown in the image to the left. A permanent magnet rotor is supported within a coil. When the coil is energised, the rotor tries to turn to align itself with the field developed by the coil. This develops a torque in the bistable rotary solenoid proportional to the excitation current.
An iron case in the bistable rotary solenoid helps concentrate the magnetic field, reducing susceptibility to disturbance by external fields. By modifying the shape of this case, the solenoid can be made bistable, so that it turns away from the center position (towards either end position) without power applied. The bistable rotary solenoid is an extreme example of this, where proportionality is sacrificed for better efficiency and bistable function.
KEY PARAMETERS (SIZE / FORCE / POWER / ETC)
Bistable Rotary Solenoids are produced in sizes from 7mm diameter as standard, and up to 50mm diameter. Smaller or larger sizes may be possible through customization for high-volume applications.
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