Re: [Emc-users] Am I overloading the servo loop with my spi ndle encoder?

[Tom]

Sebastian Kuzminsky  writes:

...
> 
> Are you using m5i20 (hostmot) or hm2_pci/hm2_5i20 (hostmot2)? 

Sebastian,

I am using the m5i20 (hostmot) version at this time. 

After talking to Peter on the phone today, it looked as if I might be looking
for a more mundane problem such as noise and/or signal integrity interfering
with the spindle encoder data stream. Sure enough, it took nothing more than a
volt meter to ferret out the problem. I was powering the spindle encoder through
about 15 feet of ribbon cable, and the voltage drop near the encoder (4.32V) was
enough to cause a loss of signal integrity at higher speeds. The encoder is nice
older unit with thru-hole components and I am sure that the insufficient Vcc/Gnd
was enough to cause some quadrature phase shift, which I witnessed on the scope.
Oh well, problem solved!

Jeff, 
Thanks for the info re: the filter being hardcoded in hostmot. Peter and I were
wondering about that. There's another reason to start planning to upgrade to
hostmot2.

Kirk,
Yes, I am using a Danfoss vfd, which is capable of switching at very high speeds
and comes with excellent ferrites on the motor outputs, and reactor filters on
the dc lines, which makes for a big & heavy unit. I checked the motor leads by
waving the scope probes near them, and there is a short length of unshielded
cable that emits detectable emi, but it is no where near the logic level lines.
All the logic/signal lines seemed clean on the scope, but who knows what ultra
high freq junk lurks there... I have an older 150mHz Tek 2445, and I could see
some "fog" at the small time slices.
I re-configured the vfd core switching frequency to a lower 8kHz to see what, if
anything that might do, and it didn't seem to hurt or  help... it just makes a
nice audible turbine-like whine now when the spindle spins up. 

A huge "Thank You!" to all for following and helping with this. 



--
SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada.
The future of the web can't happen without you.  Join us at MIX09 to help
pave the way to the Next Web now. Learn more and register at
http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Am I overloading the servo loop with my spi ndle encoder?

[Tom]

John Kasunich  writes:

... 
> If you want to use Free software, either connect your computer to the
> internet, or deal with the extra steps needed to get Free software from
> the internet to your disconnected computer.
> 
> (end-rant)
> 
> Regards,
> 
> John Kasunich
> 

John,
I hang my head in shame...
But, nice rant! I completely agree. 
I already measured and called for the price, going out now to get it. I'm going
with teflon covered cat6 cable. I will just lay in on the ground for now. 
To be honest, a non-networked robot is a very lonely (and less productive)
creature...
regards,
Tom




--
SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada.
The future of the web can't happen without you.  Join us at MIX09 to help
pave the way to the Next Web now. Learn more and register at
http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Am I overloading the servo loop with my spi ndle encoder?

[Tom]

Sebastian Kuzminsky  writes:

> 
> The new pin is called "encoder.XX.velocity".
> 
> It's documented in the hostmot2 manpage, which gets installed when you 
> install emc2.deb, and also available here:
> 
> 
> 

Sebastian,

My machine control computer is not networked and I only have a USB thumbdrive to
transfer files. I am going to have to either rip it out of the machine to
upgrade it, or jump through hoops to install the build essentials, then
recompile ver. 2.2.8 from the source package. Grr 

Tom







--
SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada.
The future of the web can't happen without you.  Join us at MIX09 to help
pave the way to the Next Web now. Learn more and register at
http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Am I overloading the servo loop with my spi ndle encoder?

[Tom]

Tom  writes:

> I will look at
> the outputs on the scope tomorrow. Also, I connected my cable shield to power
> ground in the computer ribbon cable, so that may be causing excessive noise
> feedback. 
> You have to jumper the Mesa 7i33 for differential inputs, and I think it  has
> noise filtering. 
> 
> Thanks,
> Tom


Well, I checked the differential encoder outputs on a scope on the machine while
running, and they are clean as a whistle all the way up to max motor rpm. I
re-routed the cable shield to chassis Gnd instead of power Gnd, and that helped
a little.  

My pyVCP spindle speed bar display (the one that jumps around above 3000rpm) is
linked to "rev-scaled" which runs in a slow thread. I may need to adjust the
thread timing, and route the raw encoder counts through a lowpass filter. 

Tom


--
SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada.
The future of the web can't happen without you.  Join us at MIX09 to help
pave the way to the Next Web now. Learn more and register at
http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Re: [Emc-users] Am I overloading the servo loop with my spi ndle encoder?

[Tom]

Stephen Wille Padnos  writes:


> I think there's something off in your calculations :)
> 
> 2000 counts/rev * 3000 revs/min = 6,000,000 counts/minute
> Dividing by 60 gives 100,000 counts/second at 3000 RPM, at 6000 RPM it 
> would be 200 kHz.

Stephen,

I forgot to mention that I have a 1:1.5 step up pulley driving the spindle.
Motor top speed is limited to 3,540 right now, so that is where I got my 120 
KHz.
 

> Are you sure the encoders are up to it?  Do you have differential or 
> single ended encoders?  Is there noise filtering on the encoder lines?

The encoder is a older Northern Precision Labs differential model. The line
drivers in the encoder are DS8830N(s) - I checked the driver's output full wave
propagation delays which are approx 35 ns max, which should be good for 250KHz.
I could not find a spec sheet on the encoder itself. It is likely that the
encoder has a bandwidth limitation that is causing my problem. I will look at
the outputs on the scope tomorrow. Also, I connected my cable shield to power
ground in the computer ribbon cable, so that may be causing excessive noise
feedback. 
You have to jumper the Mesa 7i33 for differential inputs, and I think it  has
noise filtering. 

Thanks,
Tom





--
SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada.
The future of the web can't happen without you.  Join us at MIX09 to help
pave the way to the Next Web now. Learn more and register at
http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/
___
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users