Re: EHP External Hardware Proposal

It seems that most of the companys that sell data aquistion
and control products list, LPT/Printer port compatible I/O
systems. Would this be the type of board that would be
considered for EHP?

Steve

----------
From: Bertho Boman <boman@...>
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO]EHP External Hardware Proposal
Date: Tuesday, February 01, 2000 5:32 PM

From: Bertho Boman <boman@...>

More thoughts:

I think Hans is going full speed but we need to talk about our goals.

A few of my suggested goals:

Keep it simple and do not reinvent the wheel. Make it possible for persons
to either use what is commonly available or easily
modifiable.

To make an external multi-axis, coordinated controller board is a
significant undertaking. To further complicate it by adding
the servo/stepper amplifiers on board would be a very large task to say the
least. Besides the hardware there would be tons of
software required.

Doing a one channel DSP (or Micro-P) based controller like I described is a
reasonable group project. That would separate the
motion control software from the servo amplifier and the tach feed back and
it would also remove the need for an expensive
custom PC I-O card. Actual I-O could be either through the parallel port
or even opto isolated RS-232.

The software to drive it only needs to be modified slightly: Instead of
writing the the command to the PC I-O card D/A it sends
it out on the printer port or the equivalent step speed command. Instead
of reading the shaft encoder counter on the I-O card
it reads it from the printer port. I think it would be relatively easy to
modify CNC software to do the above.

That means multiple existing software could be used with slight
modification since none of the timing or feedback loops are
changed for the software. Only the local servo constants would be modified
but they are normally external anyhow.

Neither Hans or I are happy to have to fiddle with Linux but if the
installation and RT kernels issues are streamlined, EMC
would be an excellent choice for the software. That would also remove the
need to modify EMC to make it work well with
steppers. An other possible alternative would be if Hans or someone with
the right experience can take a look at what it takes
to run EMC under a slightly modified NT to get reasonable RT performance as
I mentioned in a previous post.

A small single channel board with PWM amps that can be used with either
steppers or servos sounds good. Hey, stack up six of
them and we have a hexapod! It would solve several problems:

1. Pulse generator for steppers with no frequency limit or jumps
2. Amplifiers for plain steppers.
3. Encoder feedback for steppers.
4. Servo Amps with digital gain/ filter control.
5. Encoder, home and limit switches interface.
6. Electronic tach for servo feed back
7. No PC I-O card required
8. Easy opto isolation
9. Since it is a very low cost single channel board it can be used for
simple motion control of just about anything.

To the EMC "crew": Is it practical what I suggest and would you be willing
to support it?

Hans and Windows programmers: Have you taken a look at what is required to
run EMC on NT?

Who has DSP experience?

Step up to the mic. Let your suggestions and comments be heard!

If this is pulled through, I can have the boards built on my production
lines at cost (I'm not in this to make money) as long as
we can run a reasonable size batch each time. That way, software and
non-electronic persons still can be part of a large group
and we can standardize our effort.

Bertho Boman
=======================================

> From: "Carlos Guillermo" <cnk@...>
>
> Hans -
>
> I've got a pretty basic question. Are we talking about offloading
> interpolation duties to external hardware? As in sending an arc-move
> command to the external micro and then letting it execute the coordinated
> motion? Or, are we talking about merely updating a count register for

each

> axis' "commanded position" and letting the external micro handle the

servo

> loop, PID gains and all? Or, are we just talking about blind stepper

pulse

> train generation...? I think I've heard a little of each from the

various

> people interested in this system architecture, and was just wondering

what

> the external micro's duties would be.
>
> Carlos Guillermo

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