Inner working of a linear actuator

[geft]

I need to describe the working mechanism for the following actuator.

Here's what I've written so far:

Current is applied to the solenoid in order to induce magnetic fields within the actuator in accordance to Ampere’s Law. Since the plunger has high permeability, the magnetic fields produced would be strengthened and confined to the actuator. The fields produce a force which in turn moves the plunger horizontally.

However, I feel that I'm missing something. In particular, how is the force that moves the plunger generated? Is it really due to the magnetic fields? I know of the right hand rule where force points away in the direction of the palm but according to that rule, the force should actually point in the direction perpendicular to the supposed plunger movement. Is it driven by the mmf?

 

[jrlaguna]

The simplest way to consider it is through energy: the more "plunger" you have inside the coil, the lower the energy. Force is just the spatial derivative of the energy, so it enters. In fact, in absence of friction, it will just come out the other side and oscillate.

An "Ampere law" version is more complicated, seriously.

 

[geft]

But where does that energy come from? Since this actuator is driven by current, how does the total electrical energy change with respect to the size of the plunger inside?

 

[jrlaguna]

When putting current through the coil, you need some energy to fight dissipation, and also some energy to create the external magnetic field. The energy of the magnetic field is proportional to the permeability times B^2, integrated to all the volume. When you put the plunger inside the coil, the magnetic field is cheaper to maintain.

 

[geft]

I see, but why do we need energy to fight dissipation? I thought dissipation is due to energy?

 

[jrlaguna]

Don't worry about dissipation to understand this, even if it is not present, the plunger will feel the force inwards.

In any case, dissipation is due to Joule effect: dissipated power = intensity times voltage drop...