I've hooked the encoders to the parport right now just to see if I could get
that feedback working directly from the encoders to the parport. My goal is
to get closed loop motion out of my motors without having to buy a card like
a mesa. I think that if I can use the PWM output to derive an analog Vcmd
for the servo amps, I'll be able to run it, slow enough for a parport to
keep up with the encoder.
I have the mill, the original control has been ripped out of it after it had
a runaway on Y during a tool change (Y and Z axes are mounted on a gantry
like, and X is under the table)
I've only been making enough money to pay the bills and keep the car puttin
along, so I havnt been able to invest any money into the m5i20 and 7i33
combo, but I sure would love to be able to get it running at minimill speeds
with like $20 worth of hardware. buying 40 taper tooling definitely wont be
easy, I might end up turnin some of my own if i have to.
On Sat, Aug 9, 2008 at 11:54 PM, Kirk Wallace
<[EMAIL PROTECTED]>wrote:
> On Sat, 2008-08-09 at 22:34 -0400, Jim Coleman wrote:
> > Tonight I hooked up the jogwheel and one of the motor's encoders (100
> > line and 2500 lines) to the parport, and with turning up the ferror in
> > the ini I can use it like a DRO, turning the encoders moves the axis
> > readings. I was wondering if i could just build an H bridge or
> > similar switching circuit to run the output between the -12 and +12V
> > rails on an AT or AT power supply, maybe use 7809 and 7909 regulators
> > to keep it below 10V, to run to the analog VCMD input on the servo
> > amp? the manual to the mill says that it runs +/- 9V, which seems odd
> > compared to everything else. Then I'll have to likely put in a couple
> > switches on the a and b's of the encoders to send the quadrature to
> > both the amp and back to EMC. If I managed my math right, if i can
> > get the parport sampling at 30 khz (i think i read somewhere that that
> > should be realistic) I should be able to keep track of 180 RPM or so
> > on the encoders, if everything stays ideal.
>
> It sounds like you want to go directly from a jog wheel to a motor
> driver for axis movement. Then have EMC as a DRO. If that is the case,
> why not have EMC2 do the motion control and do manual machining with the
> jog wheel through EMC2? This is the normal setup. The hardware would be
> the same except you wouldn't need to build an encoder to motor drive
> interface. This could be tricky because the jog wheel is a position
> device and the amp input is a velocity signal. One unit change on the
> jog wheel doesn't correspond to a particular amp signal.
>
> I would look into setting up EMC2 to have a two parallel port pins for
> PWM Forward and PWM Reverse. Each of these could feed an opto-coupler
> that would switch your +9 or -9 Volts to convert them to a PWM modulated
> analog signal for your amp input. I am not sure of the details, and
> there might be vastly better ways to do this, but this is just to convey
> an idea of how EMC2 could output a voltage (velocity) that your amps
> need and have EMC2 do the position thing from the encoder feedback.
>
> > Also, what do I need to add in the hal and everything to enable an
> > index on the encoders? I'm thinking I can see if it is missing counts
> > if I have an index to reference.
>
> I think you would need to write a custom component that reads the
> software decoder counter on the first index trigger and then compares
> that with subsequent counts on index to see if they happen on multiples
> of encoder counts per rev. I wouldn't mind seeing more background error
> checking of hardware subsystems.
>
> > I hope all of this makes sense, its been a long day and I'm excited
> > I've actually made a little progress.
> >
> > Thanks guys,
> > Jim Coleman
>
> Are you doing more than one project? I thought you where well along on a
> mill conversion. Could you give us a summary of what you are doing?
>
> --
> Kirk Wallace (California, USA
> http://www.wallacecompany.com/machine_shop/
> Hardinge HNC/EMC CNC lathe,
> Bridgeport mill conversion, doing XY now,
> Zubal lathe conversion pending
> Craftsman AA 109 restoration
> Shizuoka ST-N/EMC CNC)
>
>
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