Linear Induction Motors

What a LIM is

A linear induction motor is simply a rotary motor unrolled and laid out flat. Rather than spinning a field inside a round stator, a straight primary — the powered part — sets up a magnetic field that travels along its length. That travelling field passes over a nearby conductive plate, the reaction plate, and drags it along. One part carries the primary; the other is just a passive conductor. The force is produced across an air gap, so nothing needs to touch.

How thrust is produced

In normal motoring, the travelling field runs a little faster than the reaction plate. That small difference in speed is what induces currents in the plate, and those currents are what create the thrust that pushes it along. In practice the running gap, the plate material and the speed all affect how much thrust you get, which is why we model each design properly rather than rely on a single rule of thumb.

Single-sided vs double-sided

There are two main layouts. They differ in whether the plate is worked from one side or from both, and that choice shapes the rest of the machine.

See it in motion

From a single primary to single- and double-sided machines, and the travelling field driving a vehicle.

Primary on the vehicle or on the track

The powered primary can sit on the vehicle or be built into the track. Which works out best comes down to how many vehicles run and how much of the route is active at once.

• Primary on the vehicle. Each vehicle carries its own primary and a passive conductive rail runs the length of the track. This needs the fewest primaries, but you pay for rail all the way along.
• Primary in the track. The primary is built into the track and the vehicle carries only a light passive plate. The vehicles stay simple and unpowered, but the whole active length of track has to be built and powered.

Reaction plate materials

Choosing the reaction plate is a design and performance decision, set by the duty it has to perform. Aluminium is the usual starting point, light where the plate is the moving member. But no single conductivity is best everywhere: the right choice depends on the slip and speed range, with a more conductive plate suiting some operating points and a more resistive one often the better match at others, so we tailor the plate to where the motor actually runs.

What we need to get started

The more of the following you can tell us, the more realistic our first design will be. Rough figures are fine to begin with.

• The job: the thrust, top speed, acceleration and mass you need to move.
• The route: distances, gradients, stops and how often the cycle repeats.
• The space available for the motor and track.
• Any existing rail or plate we have to work with — or a free hand to specify one.
• The power supply available.
• Any limits on heat, weight or cost.

What Axis delivers

We size the motor using proven equivalent-circuit models, cross-check it with detailed field simulation (FEA), and run the full route and thermal behaviour in simulation before any metal is cut. You get a specification you can build to, a clear picture of how the motor performs at speed, and the reasoning behind the design. Where it helps, we also advise on the drive and how the motor fits into the wider system.

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