Re: EHP External Hardware Proposal

Relpy in text

Bertho Boman wrote:

> From: Bertho Boman <boman@...>
>
> More thoughts:
>
> I think Hans is going full speed but we need to talk about our goals.

Well not really, I have been planning something like this for several months...

>
>
> 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.
>

I understand..

>
> 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.
>

That's not what I was intending

>
> 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.

I'm not for the DSP stuff, only becasue I don;t have the equipment. I worked with a TI DSP project, even down to crocc checking the
code for it, but the entry $$$ is very high .
It's also an over kill, at least for what I'm thinking about...

>
>
> 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.
>

Well that depends on the approach..... Before this thread started, in my original plans would have written my own g-code
interpreter, as I realized there was nothing out there that I could rely on, that is to say nothing that used the serial port and
published the protocols... So it would have been a do it my self deal.

>
> 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.

I'm not worried about existing software. In fact most of it uses the printer port, it sounds to me like you think we are proposing
some kind of hardware for the existing software and the printer port....... I'm confused....

>
>
> 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.

As I posted earlier, outboard hardware doing the pulse generation, driven my RS-232 ( or later USB simple conversion for the
Program) the outboard
hardware can stack a whole series of commands and related data, thereby "smoothing" the jerky response from ANY operating system (
even Mac)

If I understand it correctly a version of EMC does exist for Windows NT ? or did I get the wrong message ?

>
>
> 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:
>

As I said earlier, I'm doing steppers, if I close the loop all well and good. But I don't think we should run before we can walk...

>
> 1. Pulse generator for steppers with no frequency limit or jumps

OK

>
> 2. Amplifiers for plain steppers.

NO, most people already have Stepper driver hardware. The idea is not to make a new driver, just use the step and direction hardware
that most people already have, and make the new external hardware "pin compatible" with the current flavor as used by Dan Mauch's
design which is by enlarge the same pins out that was used by the old DanCad...

>
> 3. Encoder feedback for steppers.

That can be done.

>
> 4. Servo Amps with digital gain/ filter control.

Not me ...

>
> 5. Encoder, home and limit switches interface.

That can be done, No problem.

>
> 6. Electronic tach for servo feed back

Not me...

>
> 7. No PC I-O card required

I agree 100%

>
> 8. Easy opto isolation

That's where RS-232 would be easier to Isolate... Although it's a bipolar signal there are less line to isolate.. than is the case
of the printer port.

>
> 9. Since it is a very low cost single channel board it can be used for simple motion control of just about anything.
>

Well that does not apply becasue there will be no driver of any kind.

>
> 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?

I can do DSP, but don't want to put in the money for the development hardware... and it's not needed. If more horsepower is needed I
could consider the new PIC18 series...

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

Just did..

>
>
> 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.

That's nice, it should not be an expensive board at all, I expect two sided will handle it...

Hans W

>
>
> 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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