Re: [CAD_CAM_EDM_DRO] Re: Position counter stop updating....

Babar wrote:

> Hi Forum
>
> We are still in trouble with this counter stuck/hang
> problem. now this problem has become a headache and
> soon it'll become a nightmare for us. I guess i wont
> be able to sleep well soon!!
>
> We are using STG-II board the latest version of stg.
> Does these still have this noise problem with their
> Position counters??

I don't know. I know that the STG-I had a problem, when the
counter last read 000000000 and rolled over to 111111111
or vice versa. Since this is something that happens internally
to the US Digital 7166 encoder counter chip, it may be a flaw in
the chip, not the STG board. Or, there may be some timing
quirk of the STG that makes this flaw in the chip show up.
No one has really spent any time trying to track this problem
down to the exact component responsible. I believe the
STG-II uses the US Digital 7266 chip, which may or may not
have a similar problem.

> After reading Jon's mail I got into my ini and looked
> for CYCLE_TIME variable. It was found that this
> variable is present
> in many sections:
> [DISPLAY]
> [TASK]
> [TRAJ]
> [AXIS_X]
> [EMC_IO]
>
> I had set this to .001 to task, traj, and to all three
> AXIS_X but still having the same problem.

I don't think you want task and traj all running at 1000 Hz.
That may overload a medium-speed CPU with too much work.
I think the task is .01 Sec and traj is .005 Sec on my systems.

> We have connected the Encoder connections to STG-II
> board without any filteration using RIBBON cable.
> Although the connections of encoder from DC-Motors are
> made using a shielded cable.
> Encoders of all the three DC-Motors are powered (+5V &
> GND) from STG-II.

Ah, this may be the problem. I suggest moving the motors manually,
while displaying actual position. If you never see the lockup of
the display this way, it is most likely caused by electrical noise
being picked up by your unshielded wiring, and causing a huge
number of counts to be detected by the encoder counter chips.
This can trigger the code to suppress a false position reading.
But, of course, it is not a transient bad reading, it is a consistant
reading that has changed a great amount suddenly. The program
will not recover unless you wind the encoder back enough counts
(and you don't know which way to go) to get back to the original
count value.
If your encoders have differential outputs, I suggest you hook these
up to the STG board. If not, you need to shield the cables all the
way to the PC. You may also get a benefit by connecting a capacitor
of .1 to 10 uF at the DC power input terminals of the encoder, right
at the encoder. Also, check the power supply voltage at the encoder.
If the encoder draws too much current, it may cause the polyfuse
in the STG card to drop the voltage to the encoder(s).

You should also check the voltage of the encoder signals at the STG card.
It should swing from nearly zero to at least 4 volts as the encoder is
moved very slightly. Some encoders have open-collector outputs, and
don't provide any current to pull the outputs to the + voltage. If you
see a signal going from 0 to +1.6 V or so, and no higher, add a 1 K Ohm
resistor from the +5 V to each encoder signal. Check the voltages again,
they should come much closer to the +5 V level.

Jon