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

Babar wrote:

> Hi Forum
>
> We did many changes to our EMC system but still
> having the "Position Counter Stucking Problem"
>
> After reading various suggestion we did the following
> changes:
>
> 1. Converted the single ended encoder signals to
> diferential signals
> using 75174 ic. These modules are placed very near to
> Motor encoders.
> just about 2-3 inch away
>
> 2. We are now powering the encoders from an external
> +5V suply. We are
> already using 0.1 uf capacitors to dump noise at the
> output of the Power supply & the powersupply
> connections of 75174 modules.
>
> 3. In our system digital, Analog ground and earth
> connection are at the same point. We can not separate
> these AGND and DGND separate because of
> the internal construction of our servo drives and
> STG-II card.
>
> We ran the stg2diag utility program and still see
> unwanted/ strange big
> count values on each axis. this happens even when the
> slides are not moving however when we cut power to the
> machine and only keep PC ON then we dont see any such
> kind of unwanted / big values, the counters
> just keep stopped.

OK, now we have a real diagnosis! When you say only keep PC on, do you also
have the separate power supply for the encoders still on? It sounds like there is noise
from the servo amps that is causing the encoder signals to be contaminated.
My servo amps have LC filters on the output, so that no more than 1 Volt of the
100 KHz chopping waveform is allowed to escape the servo amp. What brand of
servo amp is used in this machine? I don't have to ask if the output is filtered, it
almost certainly is not. Unfortunately, adding an output filter may not be easy,
at least without retuning the servo amp. But, you would want to put inductors of
probably several hundred microHenries in series with each motor output lead
from the amplifier, and then a capacitor of perhaps .5 uF to the DC power supply
ground from each motor wire. Without knowing the PWM chopping frequency and
the motor current, it is hard for me to be more specific about this.

> Is it just a noise problem or is this may happen due
> to any wrong entry in the ini? should we post our ini?

It almost certainly is NOT a problem with the .ini file. One possibility is to change
the wiring location of the encoder signals. If the cable shield is grounded at both ends, this
is incorrect practice. The encoder cable should be grounded only at the STG card end.
Using an external power supply may be counterproductive, you may do better with the
internal power source from the STG card.

Especially since the stg2diag ALSO shows the same problem when the servo amps are
on, EMC is not to blame. And, in fact, nobody else's software will run, either.

Jon