Magnetic actuators & motors technologies
Magnetic Actuators are using magnetic effects to generate forces and generally to induce the motion of a part of the actuator.
A first large family of magnetic actuators is based on the magnetic forces acting at distance, the Laplace-Lorentz forces and the reluctance forces. Linear types offer strokes in the range of 1 to 20mm, and are complementary to piezo actuators. They can be sorted in 3 classes :
- Moving coil actuators : Placed in static magnetic field, a mobile coil driven by a current is submitted to the Laplace-Lorentz force. This force is proportional to the applied current. Thus these actuators are controllable. As there first applications were loud-speakers, they are also called voice-coils. Cedrat has designed voice coils for various automotive, industrial or space applications.
- Moving magnet actuators : Placed between two magnet poles, a mobile permanent magnet can be switched for one pole to the other using coils. Such moving magnet actuators are bi-stable. They present high forces but are not so controllable. Miniature devices have been developed by Cedrat for locking and haptic applications.
- Moving iron actuators : A soft magnetic part placed into a coil system will naturally move in a way to minimise the system magnetic energy. In standard electro-magnets, this reluctance force is larger than Laplace-Lorentz force but is only attractive and thus it is not controllable. New Moving Iron Controllable magnetic Actuators so called MICA, developed by Cedrat thanks to Oseo, are innovative biased (polarised) electromagnet actuators where the force can be reversed all along the stroke. For example they are used for generation of vibrations or for active damping in embedded applications. They offer larger stroke than piezo actuators. They offer higher forces and much less heating than Moving coil actuators.
A second family of magnetic actuators is based on magnetically-controlled active materials. Two types well are used at Cedrat for innovative devices :
- Magnetostrictive actuators : These actuators uses the magnetostrictive effect, which consists in the deformation of a magnetostrictive material when subjected to a magnetic effect. For example magnetostrictive deformation of Terfenol-D achieves 1600ppm, making of this active material an interesting competitor of piezoelectric ceramics for high power transducers or low voltage actuators.
- Magneto Rheological Fluid Actuators : Magneto Rheological Fluids (MRF) can solidify when subjected to a magnetic field. This effect can be used for making various MRF-based actuators : valves, brakes, clutches, semi-active dampers, smart hydrostatic / hydrodynamic bearings…
A third family of magnetic actuators is the electromagnetic motors also called electric rotating machines. This family is broad. So Cedrat is developing mainly small electric motors, especially Brushless DC motors (BLDC) and stepper motors.
These technologies are presented in the examples presented hereafter. Also available for linear magnetic actuators is the Catalogue of New Magnetic Actuators.
| Single Phase Stepper Mini-Motor: SPSM-1 |
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| Description: | A single phase stepper mini-motor featuring axial tunable air gap and flat magnet has been developed |
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| Applications: | Micro-Motors, Micro-technologies... | |
| Status: | Proof of concept | |
