What are Reluctance Actuators?

Reluctance actuators generate force by pulling ferromagnetic materials toward electromagnets, no permanent magnets needed. When current flows through coils, the magnetic circuit creates an attractive force that moves a ferromagnetic shuttle or armature. The principle is elegantly simple and offers compelling advantages: extreme force density and exceptional energy efficiency.

Unlike voice coil or Lorentz actuators that rely on permanent magnets and moving coils, reluctance architectures concentrate magnetic flux in the air gap, producing significantly higher force per unit volume. This makes reluctance actuators ideal for applications demanding high force in compact spaces, from semiconductor wafer stages to precision optical mounts and vibration isolation systems.

The physics of reluctance has been understood for many decades. Yet despite clear performance advantages, reluctance actuators remained confined to niche applications. The reason? A fundamental control challenge that made them impractical for precision motion systems.

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What makes reluctance actuators so hard to control?

The challenge with traditional reluctance actuators lies in their inherent nonlinearity. Reluctance force is inversely proportional to the length of the air gap, meaning force increases exponentially as the actuator reaches its maximum stroke. This creates a "pull-in" instability: as the armature approaches the electromagnet, attractive force grows rapidly, making precise position control extremely difficult.

This nonlinearity has prevented reluctance from competing with linear actuators like voice coils in precision applications. Engineers attempting to use reluctance faced:

Complex control algorithms requiring extensive system modeling and parameter tuning
Position-dependent dynamics that changed dramatically across the stroke range
Instability at high precision where small position errors cascaded into oscillations
Long integration cycles demanding custom firmware for each application

The result: reluctance actuators remained relegated to simple on/off applications (solenoids, contactors) or highly specialized systems with dedicated control engineering resources. OEMs designing semiconductor equipment, optical systems, and precision instruments couldn't justify the integration cost and risk, even when reluctance offered superior performance on paper. However, that has been changing up until recently in the last few years.

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How Fluxthor solves the complexity of Reluctance Actuators

The industry's default response to reluctance nonlinearity has been computational brute force: real-time flux estimation, adaptive control algorithms, and high-bandwidth current loops. This works but at a cost. Complex control demands expensive electronics, specialized engineering expertise, and extensive tuning for each application. The actuator becomes hostage to its controller, adding layers of overhead that complicate the system architecture.

The Invention of Reluctance Tuning

By utilizing a patented coil-free architecture, we eliminate the primary source of thermal instability, Joule heating. While traditional actuators struggle with losses, our design maintains static high-force with zero heat dissipation. This thermal stability is critical for accuracy; by removing the thermal gradient, we allow the actuator to go beyond nanometer precision, as there is no heat-induced structural expansion to compromise the position.

How we engineered the solution

The result is an actuator that delivers high force density, smooth motion, and predictable hysteresis problems, all while remaining controllable with our in-house developed servo drives. We solved the thermal and nonlinear challenges at the physics level, by using holistic loss models, flux observers and complex adaptive algorithms. This delivers plug-and-play precision, unlocking the massive benefits of reluctance performance for high-speed and high-precision markets, delivered at scale for everyone to integrate.

Patent protection

This invention is protected by two patent filings covering the coil-free magnetic circuit and the reluctance tuning methodology. These patents secure Fluxthor's proprietary position in quasi-static zero heat dissipation actuation, specifically focusing on how we switch and adjust magnetic resistance to generate force without the energy losses associated with traditional electromagnetic coils.

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