RE:New project...PCI based servo control board

[jmkasunich-at-ra.rockwell.com]

Craig Edwards wrote:

> Actually, I started on a project around a year to
> define and build a PCI based servo control board,

> I've tried to solicit some feedback for requirements
> on a couple of other forums, but most were/are
> interested in a more "distributed" sort of solution

> Anyway, I'm thinking this group might be more interested
> in this project; if so, I would like to try to attend
> NAMES just to meet some of you and to better understand
> requirements for the "ideal" servo / encoder interface
> board that could be easily used by EMC.

I'm interested, both as a potential customer and a
potential contributer.  Are you aware of Jon Elson's
universal stepper controller and PPMC board set?
The stepper contoller has 4 high speed pulse generators
and 4 encoder counters, as well as some general I/O.
The PPMC set is more modular, and includes an encoder,
input board, analog output board (for analog servo amps),
and generic digital I/O.

One of the problems that face any hardware solution is
the wide range of requirements.  Some folks have analog
servo systems, and need analog outputs with encoder
feedback.  Others are using Gecko style step-and-direction
servos, and need pulse train output, with optional encoder
feedback.  Others are using steppers, and simply need
pulse outputs.  Then there are all the secondary functions:
Jog wheels need an encoder input.  Lathe spindles also need
and encoder input, with an index pulse for threading.
Rigid tapping on a mill also needs a spindle encoder.
Variable speed spindle drives need an analog output, even
if the rest of the axis drives are step and direction.
And every system needs some amount of digital inputs and
outputs, for limit switches, e-stops, tool changers,
spindle and coolant control, and so on.

For example, consider my project.  I am trying to CNC a
Shoptask 3-in-1 machine.  I want to do a first class job,
with support for threading, variable speed spindle drive,
etc.  My requirements are:

Three main axis (X, Y, Z), with Gecko microstepping drives.
One aux axis (rotary table or index head), also Gecko stepper.
Each of these axis needs a pulse generator, and probably a
pulse counter (unless the generator is open-loop accurate).
Each axis also needs at least one and up to three inputs for
limit and home switches.  I also need an encoder input for a
jog wheel, and an encoder input (with index pulse) for the
lathe spindle.  I will be using a VFD for the spindle drive,
so I need start, stop, forward/reverse, and speed reference
signals for the VFD, as well as two signals to control
contactors to connect either the mill or lathe motor to
the VFD output.  Finally, the Shoptask millhead can be raised
or lowered (in lieu of a knee), and at a minimum I want an
encoder to tell the control where the head is at.  Control
of the head with up and down outputs would be better.  (It
is driven by a reversible gearmotor, and never moves during
a cut.)  I haven't thought too much about coolant yet, but
I certainly want to be able to add it.

So there is my list.  I'd like to collect as much input from
others as possible - what combination of encoders, analog
outputs, pulse generators, digital I/O, etc., are needed for
different types of projects?

Does anyone have any creative thoughts on how to mix and
match these functions?  I know of two basic approaches,
and Jon Elson's products demonstrate both.  First, you
can go modular.  Jon did that with the PPMC line, where
one board has 4 analog outputs, one has 4 encoder counters,
one has digital I/O, and so on.  On the plus side, you can
mix and match the stuff you need.  On the minus side, the
cost is high because you need a number of individual boards
as well as a motherboard.  Jon's Universal Stepper controller
takes the other approach.  It has a fixed set of functions
in one FPGA, on one board.  That means a lower cost, but if
you need one more encoder, or whatever, there is no simple
expansion path (other than adding another whole board).

I'd like to discuss options, and possibly come up with an
open hardware design.  I am willing to do circuit design,
board layout, etc.  Craig also seems willing to work in
this area.  Maybe we can come up with a design that is
both flexible like a modular system, and cheap like a
fixed system...

John Kasunich