On Wed, 11 Jan 2017, Gene Heskett wrote:
> Date: Wed, 11 Jan 2017 21:50:19 -0500
> From: Gene Heskett <ghesk...@shentel.net>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: emc-users@lists.sourceforge.net
> Subject: Re: [Emc-users] Two questions.
>
> On Wednesday 11 January 2017 13:34:50 Peter C. Wallace wrote:
>
>> On Wed, 11 Jan 2017, Jon Elson wrote:
>>> Date: Wed, 11 Jan 2017 10:36:18 -0600
>>> From: Jon Elson <el...@pico-systems.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] Two
>>> questions.
>>>
>>> On 01/10/2017 10:45 PM, Gene Heskett wrote:
>>>> On Tuesday 10 January 2017 23:02:28 Jon Elson wrote:
>>>>> On 01/10/2017 08:39 PM, Gene Heskett wrote:
>>>>>> But if I hook up the halscope, the apparent quadrature error is
>>>>>> worthless due to the 1KHz servo-loop timing limiting the
>>>>>> bandwidth.
>>>>>
>>>>> Well, that's why we use hardware encoder counters, as
>>>>> sampling the quadrature at 1 KHz just isn't fast enough.
>>>>>
>>>>> Jon
>>>>
>>>> Plz elucidate Jon. Something has got to be better than this. See
>>>> the pix I posted with the last reply to Peter & the list. The top,
>>>> white trace in the halscope screen is the quadrature noise, easily
>>>> 10x the timing wibbles I see on the hitachi's screen.
>>>
>>> If you are looking at the quadrature signals at a 1 KHz
>>> sampling rate, then unless the encoder is moving quite
>>> slowly, the sampling will be too coarse. That screen shot
>>> is kind of small (you can take just a single window as the
>>> screenshot, by the way) but it looks like the duty cycle of
>>> the encoders is not 50%. That may well be aliasing, as the
>>> quadrature signals seem to be moving much too close to 1000
>>> Hz. You'd get much better results below 100 Hz. Or, with
>>> Mesa hardware, you can sample these with the base thread.
>>>
>>> I can't comment on the velocity output from the Mesa, as I
>>> don't know their gear (or driver). But, the scale is 2/div,
>>> meaning the scaled velocity output is jumping around 2 user
>>> units up and down at a KHz rate. Clearly, not good.
>>>
>>> Jon
>>
>> The velocity output is calculated by using the number of counts
>> divided by the time between the counts (time measured via a 1 MHz
>> timestamp). If you have less than 2 counts per servo period the
>> velocity estimation accuracy depends heavily the quadrature
>> phase/symmetry since the edge spacing entirely determines the
>> estimated velocity at this speed range.
>>
>> I suspect what Genes plot shows is that he has significant quadrature
>> phase/symmetry errors at the FPGA inputs.
>>
>>
>> Again here is a velocity plot of a accurate 100 Hz quadrature signal:
>>
>> http://freeby.mesanet.com/100_Hz_quadrature_velocity.png
>
> I've not played with the stepgen type 2 yet, but I have adjusted the
> quadrature a few thousandths and reduced it by about 1/3rd. Thats
> helpfull as I can filter to smooth a tach dial once I have defeated the
> noise.
>
> But I have another concern. I have had to do a full powerdown reset to
> clear a watchdog bite. The original config was I think intended to clear
> it by re-enabling the machine, but I could nolinuxcnct, so I disconnected
that
> reset in the hal file I started with as the logic was self feeding,
> locking out the ability to reset the disabled machine. And I couldn't
> even do it from the halconfig as it claimed another signal was driving
> it when I tried to setp that pin.
>
> Do you, Peter, have a logic diagram I can re-construct for that, that
> actually works?
You need to restart linuxcnc to clear a watchdog bite
>>
>>
>>
>> Peter Wallace
>> Mesa Electronics
>>
>> (\__/)
>> (='.'=) This is Bunny. Copy and paste bunny into your
>> (")_(") signature to help him gain world domination.
>>
>>
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>
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page <http://geneslinuxbox.net:6309/gene>
>
> ------------------------------------------------------------------------------
> Developer Access Program for Intel Xeon Phi Processors
> Access to Intel Xeon Phi processor-based developer platforms.
> With one year of Intel Parallel Studio XE.
> Training and support from Colfax.
> Order your platform today. http://sdm.link/xeonphi
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>
Peter Wallace
Mesa Electronics
(\__/)
(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination.
------------------------------------------------------------------------------
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Access to Intel Xeon Phi processor-based developer platforms.
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Training and support from Colfax.
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