On Tue, 31 Jan 2012, Viesturs L?cis wrote:
Date: Tue, 31 Jan 2012 19:51:37 +0200
From: "[UTF-8] Viesturs L?cis" <viesturs.la...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] US Digital encoders?
2012/1/31 Tom Easterday <tom-...@bgp.nu>:
Do you have differential drivers for the encoders or are you running them
single ended?
Single ended.
I would put the encoder signals on an oscilloscope and see what they look like
to the controller.
Since I do not have oscilloscope, it seems like HAL Scope would be the
only option. But can I see A and B inputs of encoder module on 5i23
card?
Or, it could be noise introduced into your signal driving the motors (rather
than the encoders).
That was an issue we ran into on the Plasma gantry table and
had to design some custom filters to deal with it.
I have retrofitted plasma table and IMHO in terms of generating noise
the plasma is from totally different league. Client wanted to control
the machine - jog the table and run/pause/stop g-code file - with usb
joypad.
I set them up with that option, but I know that pretty soon they
removed the joypad, because plasma was disturbing the joypad.
There are 4 wire leads for each motor - 3 phases and GND. I have
packed leads for each motor in a separate socket.
I do have power cable for spindle running along other cables, wrapped
in aluminum foil and grounded at one end , plus the spindle was not
turned on, when I tried to tune servos.
So I do not see any source for noise in motor power cables. Plus I
suppose the oscilloscope is the only way to check it.
The three phase PWM is a fair noise source. Not just capacitively coupled
noise from the three motor wires but inductively coupled noise due to current
spikes from the 28V PWM driving into the motors winding/frame capacitance.
This can be mitigated by putting a common mode choke (Big ferrite bead) over
the three motor leads (DO NOT include the ground lead)
Please try the encoder sample rate lowering example I provided. This will
quickly help to see if there is a noise problem. Noise piked up by the encoder
wires either inductively or capacitively tends to be short pulses. By
lowering the input bandwidth a lot of this kind of noise can be filtered out.
2012/1/31 dave <dengv...@charter.net>:
I also assume you use a star grounding system for your encoder
and signal cables.
Yes.
2012/1/31 Roland Jollivet <roland.jolli...@gmail.com>:
Most CAT5 cable is solid single strand, not good for installing on machines
or in vibrating environment. But maybe yours is multi-strand?
Yes - they are multi-strand, but I called them "flexible" as I did not
know the right word :)
It took me some time to find those cables, because I was looking for
shielded multistrand cables with at least 6 leads.
I do have diy converters from single ended to differential signal. It
was used to convert step and dir signals for 3 drives to differential
signal. I could use them to get differential signal.
But would it make sense not to have differential to single ended
signal decoder and feed in 7i39 only half of the differential signal?
Viesturs
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Mesa Electronics
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