Re: [Emc-users] Has anyone ever done a Kitamura MyCenter/EMC conversion?

[Jon E. <el...@pi...>]

Chris Radek wrote:
> On Fri, Oct 30, 2009 at 10:11:49PM -0500, Jon Elson wrote:
>   
>> One thing that has been common in the Fanuc systems is they use servo 
>> amps that need velocity
>> feedback from the motors, but they don't have tachs on them.  The 
>> controller synthesizes an analog
>> velocity signal from the encoder and sends that to the amps.  
>>     
>
> That sounds odd and makes me wonder (again) about something on my
> machine. 
>
> I have tachs, but they were not wired to the amps.  They went to "some
> part" of the main computer of the Yasnac control [which was missing].
> Then "something else" came from the control board and went to the
> velocity feedback input on the amps.
>   
Yup, that was the way the old Fanuc controls worked.  They used either 
the L290
or a similar quadrature to voltage converter chip.  The L290 was a 
frequency to voltage
converter specifically designed for this purpose.  It used 2 identical 
sections feeding into
a difference amp so encoder dither doesn't count as velocity.  
Unfortunately, it is no longer
available.
> I do not know what was there - it's possible they were just wired
> together.  I wired them straight through.
>
> Any guesses whether something was there?  I had some trouble getting
> stable velocity loops, and it makes me wonder.
>   
The problem is the real Fanuc machines had no tachs, so it makes the 
retrofit harder.
If you DO have tachs, then no problem.

One possible setup had a circuit that compared absolute velocity from 
the encoder to absolute
velocity from the tachs.  If the encoder velocity was 20% greater than 
the tach showed, it caused
an E-stop.  This was used in the days of encoders with incandescent 
light bulbs, where an encoder
failure was a yearly ocurrence.  The Allen-Bradley 7320 had this.

Jon