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Frequently Asked Questions

 

What is a ‘stator’?

The stator is the stationary portion of the linear motor. It comprises coils wound within slots in a core. The core is typically formed from a stack of thin sheets of laminated electric steel.

What is a ‘reaction plate’?

The reaction plate is the array of alternating-polarity permanent magnets that is attached to the mover. It can be single-sided or double-sided (where it is mounted vertically as a “fin” that travels within two stators mounted face-to-face).

Do you have a catalogue of standard linear motors?

All of our linear motors are designed and optimised to specifically meet the unique requirements of each application. We believe that it is important to adapt our designs to each customer’s requirements to offer the best possible solution and eke out as much performance from our motors as we can. Hence, we do not offer a catalogue of standard designs, although most of our motors share some common topologies and characteristics.

How efficient are your linear motors?

In a direct motor against motor comparison, linear motors are typically not as efficient as traditional rotating motors. This is because a larger air-gap is usually necessary and not all of the energised length of stator fully interacts with the reaction plate and contributes to the thrust force. However, when looking at the overall system level, in many cases better efficiency is achieved. For example, without a linear motor, gearboxes, differentials, chains, levers, crankshafts etc. are typically required, which all contribute to the overall system losses.

Do your linear motors levitate the mover?

No, our motors do not provide a levitation force. Levitation requires considerable energy input and so it is generally not energy-efficient to do so unless travelling at very high speeds. In fact, the single-sided versions of our motors exhibit a strong attractive force between the mover and the stator due to the permanent magnets wanting to stick to the electric steel of the stator core. Although this is beneficial for some applications, we normally use a double-sided arrangement to cancel out this attractive force.

Our motors need to be mechanically guided to maintain a consistent air-gap between the mover and the stator sections. For example, this can be achieved with traditional light-rail wheels and track. However, since the propulsion force is transferred magnetically to the mover, there is less wear-and-tear and there are no issues with traction (in fact, the track can even be lubricated to reduce the rolling resistance).

How robust and weatherproof are linear motors?

The linear motor stator sections are potted in an epoxy resin using a process known as vacuum-pressure impregnation and in some cases are also hermetically sealed within stainless steel containers. Also, since the copper windings are fully embedded within the stator blocks, they are well protected. Thus, the finished stator modules are very robust and weatherproof, and require no maintenance for their design life.

What happens if there is a power failure?

Our linear motors can be designed with an inherent fail-safe mode, where the stator windings are short-circuited in the case of a power failure. When the reaction plates on the movers interact with stator sections with shorted windings, currents are induced in the windings which, in turn, cause magnetic fields that oppose the motion. Thus, in the case of a power failure or fault condition on a slope, the speed of the movers are limited to a slow terminal velocity, which prevents the possibility of a runaway situation.