> -----Original Message-----
> From: Leonardo Marsaglia [mailto:ldmarsag...@gmail.com]
> Sent: March-20-20 8:49 PM
> To: Enhanced Machine Controller (EMC)
> Subject: [Emc-users] Question about index pulse on high resolution encoder
>
> Hello guys,
>
> I'm testing a phisical encoder to simulate how the spindle will work with
> the external offsets. So far so good but I need to clarify something that I
> suspect. Here it comes:
>
> The encoder I'm testing is an ERN471 from Heidenhain. A beast of encoder.
> It says 5.000 line counts on the datasheet but also says it outputs 125.000
> signal periods per revolution, so when I read it in LinuxCNC with a scale
> of 1 I find that I'm having 500.000 pulses per turn. A lot of resolution.
> I'm scaling it to 1024 since this is what I have on the Mazak.
>
> My concern is (and I think this is to be expected) that I have missing
> index pulses if I rotate the encoder too fast with my fingers. I tried to
> use a shorter servo-period and that seemed to improve things a little but
> not solving the problem always.
>
> Is this what's happening? Should I not expect this behaviour with the 1024
> PPR encoder and the spindle turning at about 200 RPM ?
>
> I would like to hear your thoughts just to be relaxed, since a missing
> index pulse on this kind of processes is likely to break the tool and
> spoil the part.
>
>From what I've read so far the LinuxCNC system only uses the index pulse when
>it starts a sequence that requires synchronized motion. The G command for
>threading sets a flag that tells the system the next time it sees and index
>pulse to clear the counter and then it cancels the flag. The G command
>doesn't restart it. At this point the A/B are tracked for direction based on
>the other operations generated by the G command.
The MESA cards, AFAIK, use a rising edge to trigger this index. After that
they don't care how long the level is or when it drops. Most interrupts into
processors work the same way. The edges are usually qualified by the processor
or system clock so it might check it a few times that it stayed high for 100 nS
before it registers as a rising edge.
So if you think you are missing pulses first I believe the HAL Scope might be
able to see it. If it doesn't then you need a real scope. Depending on the
hardware it may well need full differential signals in order to deliver the
pulse into the hardware.
John
> Thanks as always!
>
> _______________________________________________
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
