Re: Re: Re: Stepper program w/Encoders?

Alan,

Alan Rothenbush wrote:

> Hans
>
> > If you are putting a uP in there loop, why not make it figure out
> all
> > the backlash parms... including dead time!
>
> I'm not sure I know what you mean by dead time .. I DO time the
> spacings
> between the step pulses and issue the additional steps at whatever
> rate
> the previous steps were issued at. Whatever rate the CNC program
> thought
> was appropriate is what I'll be using.
>

I'm new to CNC also, by dead time I mean the time (= number of turns
needed) to move the tables when reversing direction.. As an example.
If it required (large number for example) 200 turns to move the table in
the opposite direction, it should be possible for the uP to figure this
out, because you mentioned (I think) the use of a DRO as input...

> I DON'T want to re-engineer this wheel .. I'm not sure I know enough
> about it.
>

I agree wheels are wheels..

> The current plan is for quite a simple device, just to see where it
> goes.
>
> Please understand that I'm very new to machining and newer still to
> this
> CNC business. I THINK I understand the basics, but that's about it.
>
> > I've had the idea for a while, and was going to expand it with a
> lookup
> > table to generate thread compensation, that way it would
> > move the true distance and lead screws become anything you want them
> to
> > be... It all depends on the feedback resolution...
>
> Don't the CNC programs effectively do that for you ? And that being
> the case,
> why would you add it to the uC ? Or am I not understanding things ?
>

Not the programs I'm using. They compensate for backslash ( dead time)
but do not compensate for thread distortions. With a DRO input it should
be possible to build a lookup table and then compensate for it... I have
plans...

> > I'm an electronics kind of person also...
> > Which uP are you using ?
>
> The current project uses a PIC12C509 to convert the quad inputs to
> Step, Dir,
> and Error signals and a PIC16C63 to read the switch, CNC, and Step/Dir
> inputs
> and outputs the CNC and LCD signals.
>

The 12C509 is kind of tiny for and I don;t skimp on uP's it's not worth
it. The only place I've used the 12C509 is in my Smart Current Sensor,
which you can see at my web site http://home.swbell.net/hans_w

> The first rev didn't use a 509, thinking that the 63 had enough
> interrupts
> to do the job, but a CAREFUL read of the fine print of the datasheet
> showed
> that it didn't.
>
> The 16C6x devices have 4 inputs that will generate an "Interrupt On
> Change".
> This sounds perfect to read the quad inputs, as both positive and
> negative
> edges will generate an interrupt.
>
> I dedicated this port to inputs .. 2 of the IOC inputs going to quad
> ins,
> 1 going to an EStop switch and 1 going to the Step signal from the
> CNC.
> Limit and a pair of Reset switches went to the other inputs, which
> were
> simply polled.
>
> It didn't work ! Turns out that IOC feature ONLY works if the other
> inputs
> of that port are NOT polled .. perhaps, not even used at all. The
> "feature"
> is designed for "Wakeup On Keystroke" and is not too useful
> otherwise.
>
> There were a number of solutions, but adding a $2.00 PIC was
> certainly the
> cheapest and easiest. The Clock signal from the 509 generates a
> conventional
> interrupt on 63, and this is the only interrupt used, so I'm SURE
> that I
> don't miss anything. Everything else is polled, and since the ISR
> is so
> short ( about 4uS, IIRC ), polling should be fine.
>

Sounds ok ..

> ( For a commercial product, I'd have tried harder to do it all in
> one uC,
> but when it's hours of my time to save 1 $2.00 part, forget it. )
>
> Why a 12C509 ? I have a bunch laying around and have an ICE for
> one.
> Why a 16C63 ? Exactly the same reasons as the above.
>
> In the past, I've done a lot of work with 8051s ( and things like
> them
> from Dallas and Atmel ), and still do. Slowly but surely I'm doing
> more and more with PICs, though. They're TOUGH in nasty
> environments,
> they're fast, they're predictable in that there's not THAT much
> errata
> ( assuming one actually READs the manual ! ) , there's a big choice
> of
> them, and most important to me, I can program them in an 8051-like
> version
> of assembly language. Because I program so imtermittently, both
> home and
> at work, it's important to keep the number of languages down.
>

Have a look at my 7 port serial multiplexer, it uses 8 PIC16C66's and
they are real busy !
BTW I have succesffully run the 16C66 at 40MHz and all functions
including SPI are good..

As soon as I get a window of time, I plan a projects with the above
mentioned items... and interface the uP with RS-232 that will then make
it system independent and all the fuss about Linux will be history....
I'm an NT person myself... I've been running it since beta 1... and
can't see what people want with Linux, it's a bloody nightmare of
incompatibility, much like beating oneself with for fun.! I don't think
Bill Gates has anything to worry about when it comes to Linux....!



Hans Wedemeyer

> Alan
>
>
>
>
> --
>
> Alan Rothenbush | The Spartans do not ask the number of
> the
> Academic Computing Services | enemy, only where they are.
> Simon Fraser University |
> Burnaby, B.C., Canada | Agix of
> Sparta
>
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