Tubular permanent magnet linear motors

[carpekd]

Hello all,

I'm a mechanical engineer who recently recently became interested in linear motors and generators (random, i know). I've narrowed my interest to tubular linear permanent magnet motors (servo types) such as the ones made by these people:

http://www.dunkermotor.com/default.asp?id=116&lang=2
http://linmot.com/
http://www.nitek.it/green-drive-tubular-linear-motor_prd_pr3_12_27_eng.aspx

My end goal is to eventually build my own, but my knowledge electrical motor theory is very limited at the moment. So to that end, I'm reading as much as I can and trying to soak it in, but everything I'm reading is theory based, and I want some practical construction knowledge as well. So to start, I found an old tubular linear motor (made by innovex inc.) off a transfer switch to disassemble and dissect. It looked like the basic type of motor I'm interested in (without an encoder...) but I'm puzzled by the fact that the shaft doesn't contain permanent magnets... Can anyone fill me in on how this linear motor works? I've attached a picture and I've got more of the disassembly if you need it.

 

[anorlunda]

ping @jim hardy. Spring cleaning, but you might like a crack at it. I can move it to DIY.