It seems the pick and place activity has died down, so maybe this will spark some interest. While designing my pick and place, I came across tubular linear motors. They seem very well suited for this application.
Check out: [ame=http://www.youtube.com/watch?v=MUcU6xLQQwU&feature=results_video&playnext =1&list=PL7D5F41665DA52085]Linearmotor Modules XY ThrustTube Parkem - YouTube[/ame]
After endless researching on methods of constructing them, it seems like the best and easiest way is stacking the magnets in a stainless steel tube with the same polarity facing each other WITH NO GAP. South/North-North/South-South/North-North/South, etc. This does pose some construction issues since the magnets repel each other, but that can be solved by making some additional tooling for putting the magnets in the tube and trapping them until the next magnet gets inserted.
There are also some articles about using SMC (Soft Metallic Composite) discs between the coils and forming pickup shoes for the magnetic flux. This started to discourage me, but it seems that Copley's ServoTube "Forcer" simply uses coils stacked together without these discs. It is pretty hard to find a good picture on the net as they are pretty low resolution.
Anyone know what kind of "varnish" is used to coat motor coils?
As far as I can tell, all that is needed to make a forcer is the coils spaced at 1/3 the magnetic length (at least 6 coils - a positive/negative coil for each of the 3 phases) and 3 hall sensors positioned appropriately. Controlling it would be any dumb trapezoidal torque amp, and motion controller. Of course, you would also need linear rails and guides to keep the forcer over the magnet tube, a base to mount the linear rail and end-support for the tube, and a linear encoder for position feedback to the motion controller.
I've got much more info if anyone wants to ask questions.