Hi,

I already have 1 micron linear scales fitted to my machine, so it makes sense to use them.

Agreed. As far as I am aware there are two choices to proceed, a feedback controller or load sensing servos.

If it were my choice and I chose a feedback controller I'd go with Galil, I know its expensive but you can bet it would work.
The other two would 'probably work'....but do you want to spend that sort of money on a 'probably'?, I wouldn't.
I think the CSMIO Mach4 plugin is dodgy and CSLabs don't seem to care. I hate it when Chinese companies do that
rubbish.....so why should I spare a Polish company? That leaves the Hicon, I'd want to do a deal more research
before I spent $1200USD.  Given that you've already got AC servos it seems to me like a backward step to use
them as analogue servos and use the Hicon to close the loop.

May I suggest do a bit of research on the Delta A2 series servos.

The company I bought mine from email me with offers. The latest email (deleted alas) explained that due to the volume of sales
that Delta was going to increase their discount and the company wanted to pass some of those savings on. It looked
roughly that I would save about $80USD on a 750W B2 series like I've already got OR I could have 750W A2 series
for the same as I paid for B2 series as short as a few months ago. That would put an A2 series servo/drive/cables about
$430USD excluding shipping.

http://www.ebaystores.com/fasttobuy2012

I have scanned through their listings and don't see any that match the offer they emailed me with....I would be emailing them
to get details. Just as a note Delta have a range of models that have either CANOpen OR Ethercat or some other network
combination. The network capable drives are approx. another $100USD or so. You require just the standard step/direction
units which are cheaper. That is the ASDA-A2-L drives.

https://www.deltaww.com/Products/CategoryListT1.aspx?CID=060201&PID=23&hl=en-US&Name=ASDA-A2+Series
https://www.deltaww.com/services/DownloadCenter2.aspx?secID=8&pid=2&tid=0&CID=06&itemID=060201&typeID=1&downloadID=A2+Series&title=A2+Series&dataType=3;&check=1&hl=en-US

If, after reading the user manual for the A2's, and you think it may work, would you consider buying one servo and drive to see if
you can make it work to your satisfaction?

Craig

The machine was originally going to use the CNCBrain but that project stalled before the linear encoder part was completed.
My SureServo AC Servo system can use analogue inputs, so the Galil system ought to work. However, it's very expensive and frankly they didn't seem that keen to help. There didn't seem to be anyone with experience of the system so it was too risky to follow up on.
I'm using closed loop on the leadscrew using step/direction at present with backlash compensation, but it's nowhere near are good as a linear scale would be.

Galil support probably won't spend much time with you until you buy a controller.  But their pre-sales should be able to answer any questions you may have on what is needed to accomplish what you want.  I have NEVER gotten someone from Galil that wasn't able to answer a question or be able to put me in contact with someone who could.  And I have been working with them for nearly 30 years now.  If you need to talk to an applications engineer, Vincent Nagel is one of the app engineers that I use and he's on the ball, for sure.   

Is it expensive?  That is relative.  On a typical CNC machine, say like if my Matsuura MC500 were a new production machine, the Galil controller would be about 5% (or less!) of the total cost of the machine.  A DMC4153 ($1695.00) is a good controller for a VMC.  That allows for XYZA, and analog spindle control.  For an industrial motion controller, that's a steal!!!  Have you ever priced a Delta Tau?  Again, expensive is relative and the Galil might be more controller than your machine needs.  But if you are taking about dual feedback, and let's be honest, you are no longer playing in the hobby realm of motion controllers. 

Also, Galil has a plethora of information on their website like application notes and white papers.  Here is the whitepaper describing dual velocity loops:  http://www.galilmc.com/download/whitepapers/wp_advanced_control_techniques_for_real_world_drivetrains.pdf

Standard dual loop is included with the controller, I believe.  Check with Galil to be sure.  If you want the advanced dual loop stuff, then there will be an NRE (one time engineering fee) for special firmware. 

Steve