Old Mori Seiki AL-2 retrofit questions

Hopefully this is the right area to post.  Here's the short version:  I've used LinuxCNC for a few manual to CNC conversions but my experience is limited to stepper drives and parallel port setups. I have a Mori Seiki that is in great shape mechanically.  I had it demonstrated to me by the previous owner and it all worked and we turned a few parts and drilled a bit.  He was downsizing and selling several machines.

I don't even want to use it with the current control.  I am familiar with LinuxCNC, use PathPilot on two Tormach machines, and feel it is by far the better choice for me long term.

So, I have no idea where to even start.  When I look at the MESA cards, it makes some sense and I have a 7i76e on hand to learn with.  But when it comes to getting this done, the servos aren't making much sense to me (I'm sure I'm stuck in step/dir paradigm) and how I would go about figuring out how to interface all the miscellaneous bits of the lathe such as the tool turret, tailstock, hydraulic chuck, VFD...it just quickly feels like I'm as lost as a fart in a hurricane.

Other than just reading everything I can here, which I have been doing for a while, are there any good resources to just drinking from the firehose and coming up to speed on all this stuff in a reasonably short timeframe?  I so want to use the lathe, and I know that even if I knew exactly what to do for the conversion that it will be a long involved project, but I don't really know how to start.  Any pointers would be appreciated.
 

Mesa 7i76E is a good start, it does step/dir so new servo drives work also, it does have a spindle output with encoder feedback, so damn near perfect. That "near" can be removed at any time by adding an daughter board at any time, just in case you might need step/dir with glass scales.
Start by doing an inventory of what is already there, post details here, pictures help a lot, and for reading, here is everything that has anything to do with retrofit on the LinuxCNC website:
www.google.com/search?q=retrofit+site%3A...sAEA&sclient=gws-wiz

Thanks, I'll just start reading and making mistakes until I know what to ask. I also want to convert my Fadal so I need to become very knowledgeable on all of this quickly. The stepper stuff all made sense because I started with GRBL so it's hard to get that out of my head when I look at the servos. The +-10v stuff just leaves me scratching my head.

BruceCharlesDesigns wrote:

But when it comes to getting this done, the servos aren't making much sense to me (I'm sure I'm stuck in step/dir paradigm) 
 

The difference between a step/dir system and a servo system is in the PID control module. 

This sits between the position command from LinuxCNC and the HAL component that generates the speed command for the servo. (or, in some cases the torque command. Sometimes even a position command). 

A PID controller has an output of zero (or, sometimes, a steady value) when the command and the feedback match. And a varying output when they don't, with the output varying in relation to how far out of position the system is. 

It's called a "PID" controller as it has three parts, Proportional, Integral and Differential. Which sounds like complex maths, but it isn't. A PID controller is only a couple of lines of code:

The Pgain, IGain and Dgain are numbers that you choose when tuning the system. 

If you Google you will find lots of mathematical analyses of PID controllers, but in the real world folk just guess numbers and tweak them until they work. (In fact, my real job is exactly that, I make engines idle smoothly) 

So:

Stepper:
Command => step generator

Servo:
Command => PID => pwm / analogue / velocity-mode stepgen
feedback => PID

Actually, there is typically something akin to a fixed-gain PID inside the stepgen, where the output is how many steps to try for in the next servo period, and the (internal) feedback is how many steps it made in the previous servo period. 


 

What type of CNC control / Axis / Spindle drives are used?
Assuming drives and motors are in good working order, If the machine controller is very old like 3T,6T,10T, they are all equipped with analog +/-10v controlled drives.Mostly DC axis/spindle drives. Some of the 10T versions may have +/-10v controlled AC spindle drives.All later versions become more digital.
The Fanuc 0T uses 3-phase PWM AC servo. Spindle control can be +/-10v or serial spindle.
Depending on the control model your requirement will be different.

Thanks Andy, that makes sense to me. Where I get lost is where all this translates to the real world as far as connections and linuxcnc. I've decided I'm going to start taking off a few bites at a time. I'm going to get my old PM25 with steppers running with the 7i76e to get me into Mesa land instead of LPT land. Then I'll start tackling interfacing a Mesa card to the servos either in this lathe or my Fadal. We'll see how it goes.