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Re: PID loop frequency

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On 2018-10-05, tabbypurr@gmail.com <tabbypurr@gmail.com> wrote:
> On Friday, 5 October 2018 15:07:48 UTC+1, Fitzgerald  wrote:
>> I'm working on a digital PID motion controller. The target/goal is to 
>> move at (very) constant velocity. Position feedback is from a linear 
>> encoder with quadrature output. The input to the controller is a linear 
>> ramp (i.e. constant velocity) and the PID changes the motor output to 
>> minimize the error. The system works, but I'm looking to improve its 
>> performance at low velocities.
>> 
>> At low velocities there are only a few pulses from the encoder per servo 
>> cycle. In the error signal I can clearly see this quantization. If I 
>> lower the frequency of the servo cycle; the controller performance 
>> increases (i.e. smaller velocity variations).
>> 
>> Two questions:
>> - Is there a method to determine optimal servo frequency?
>> - Would it be beneficial to separate the controller in two control 
>> loops; an inner velocity loop and an outer position loop. Perhaps with 
>> both running at different frequencies?
>> 
>> Any pointers to good documentation are appreciated.
>> 
>> Thanks,
>> Fitzgerald
>
> Cassette deck motors solved this a while ago. IIRC they used a bit of negative resistance, no PID. You could switched-mode it.

The ones I dissasembled when I was doing learn by destroying had
centrifugal switches on the rotor.  but a recent thread on SX had a
circuit which did the negative resistance thing (for a record player).
if you cancel the resistance of the windings you can command the
back-emf, and thus the speed, directly.



-- 
  Notsodium is mined on the banks of denial.

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PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-05 16:07 +0200
  Re: PID loop frequency bill.sloman@ieee.org - 2018-10-05 07:53 -0700
    Re: PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-09 08:08 +0200
      Re: PID loop frequency bill.sloman@ieee.org - 2018-10-09 00:11 -0700
  Re: PID loop frequency Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-05 10:58 -0400
    Re: PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-09 08:12 +0200
  Re: PID loop frequency bitrex <user@example.net> - 2018-10-05 10:58 -0400
    Re: PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-09 08:18 +0200
  Re: PID loop frequency Chris Jones <lugnut808@spam.yahoo.com> - 2018-10-06 01:04 +1000
    Re: PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-09 08:30 +0200
      Re: PID loop frequency bill.sloman@ieee.org - 2018-10-09 00:21 -0700
      Re: PID loop frequency Chris Jones <lugnut808@spam.yahoo.com> - 2018-10-09 23:03 +1100
        Re: PID loop frequency bill.sloman@ieee.org - 2018-10-09 05:44 -0700
          Re: PID loop frequency Chris Jones <lugnut808@spam.yahoo.com> - 2018-10-10 00:01 +1100
            Re: PID loop frequency bill.sloman@ieee.org - 2018-10-09 07:33 -0700
  Re: PID loop frequency Lasse Langwadt Christensen <langwadt@fonz.dk> - 2018-10-05 08:49 -0700
  Re: PID loop frequency Jon Elson <elson@pico-systems.com> - 2018-10-05 13:59 -0500
  Re: PID loop frequency Hul Tytus <ht@panix.com> - 2018-10-05 19:52 +0000
    Re: PID loop frequency Jon Elson <elson@pico-systems.com> - 2018-10-05 15:46 -0500
      Re: PID loop frequency George Herold <gherold@teachspin.com> - 2018-10-05 18:05 -0700
      Re: PID loop frequency Hul Tytus <ht@panix.com> - 2018-10-06 18:49 +0000
    Re: PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-09 08:38 +0200
  Re: PID loop frequency DJ Delorie <dj@delorie.com> - 2018-10-05 16:19 -0400
    Re: PID loop frequency Fitzgerald <john.smith@mailinator.com> - 2018-10-09 08:48 +0200
  Re: PID loop frequency tabbypurr@gmail.com - 2018-10-05 14:33 -0700
    Re: PID loop frequency Jasen Betts <jasen@xnet.co.nz> - 2018-10-06 02:14 +0000
      Re: PID loop frequency bill.sloman@ieee.org - 2018-10-05 19:49 -0700
        Re: PID loop frequency Klaus Kragelund <klauskvik@hotmail.com> - 2018-10-06 01:19 -0700
          Re: PID loop frequency bill.sloman@ieee.org - 2018-10-06 03:26 -0700
            Re: PID loop frequency George Herold <gherold@teachspin.com> - 2018-10-06 11:56 -0700
            Re: PID loop frequency Klaus Kragelund <klauskvik@hotmail.com> - 2018-10-08 06:27 -0700
              Re: PID loop frequency Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2018-10-08 10:22 -0400
                Re: PID loop frequency Klaus Kragelund <klauskvik@hotmail.com> - 2018-10-09 14:46 -0700

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