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RE: [mach1mach2cnc] missed steps and closed loop stepper controls

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  • Dr Mark Vaughan
    I ve not kept track with everything recently Daniel, but I m sure Mariss was developing one that is fed from a modded G100, called something like the
    Message 1 of 40 , Jun 1, 2010
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      I've not kept track with everything recently Daniel, but I'm sure Mariss was
      developing one that is fed from a modded G100, called something like the
      unstallable stepper.

      This was some time back, so I assume it's operational now, though if not
      listed on their site perhaps it's still not finished.



      Regs Mark



      Dr. Mark Vaughan Ph'D., B.Eng. M0VAU

      Managing Director

      Vaughan Industries Ltd., reg in UK no 2561068

      Water Care Technology Ltd, reg in UK no 4129351

      Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH UK.

      Phone/Fax 44 (0) 1872 561288

      RSGB DRM111 (Cornwall)



      From: mach1mach2cnc@yahoogroups.com [mailto:mach1mach2cnc@yahoogroups.com]
      On Behalf Of Daniel
      Sent: 01 June 2010 07:55
      To: mach1mach2cnc@yahoogroups.com
      Subject: Re: [mach1mach2cnc] missed steps and closed loop stepper controls





      Hi Mark,

      >
      >There's even a gecko controller that can slow the feed down if it
      senses the difference between the command step position and error in each
      step (the rubber tooth area) before it reaches the point where the step is
      lost, making a stepper near as good as a servo.

      Which one is this? Nothing I can see on there website...

      Regards,
      Daniel

      ________________________________
      From: Dr Mark Vaughan <mark@... <mailto:mark%40vil.uk.com> >
      To: mach1mach2cnc@yahoogroups.com <mailto:mach1mach2cnc%40yahoogroups.com>
      Sent: Tue, June 1, 2010 12:26:27 AM
      Subject: RE: [mach1mach2cnc] missed steps and closed loop stepper controls

      Usually on simple surface CNC grinders only the Z of the wheel is CNCed

      If you make the traverse CNCed, and especially steppered, because they move
      in steps with a motion sort as though they jerked on a cog with rubber
      teeth, you'll end up with a pattern left on the ground surface.

      The main traverse is usually done with a hydraulic ram.

      A while back a UK company commissioned a project to build loads of CNC
      surface grinders that went wrong, the developers all fell out and the
      company went bust, we picked up the pieces for several firms that bought
      half faulty machines and designed a control based around a PLC together with
      what we could salvage to get them going, so we spent quite a few months with
      a precision firm developing this and learning how not to do it.

      If it's a CNC cutter grinder or other complex angle grinder then the pattern
      won't be as noticeable and you may be Ok with steppers since curved surfaces
      don't show as bad, and most others than machine items like this don't have a
      smooth finish either.

      Please bear this in mind with your design.

      As far as inputing data to proof position back to mach, there are some
      devices available, the names don't all spring to mind at the moment, but I'm
      sure someone else will remember. I think the DSPMC can do it, and perhaps
      the Galil, but there's another that's cheaper and simpler whose name I can't
      remember, usually I think they just show a fault has occurred and stop the
      program. There's even a gecko controller that can slow the feed down if it
      senses the difference between the command step position and error in each
      step (the rubber tooth area) before it reaches the point where the step is
      lost, making a stepper near as good as a servo. Personally if I'm worried
      about lost steps I either ensure I stay well below the torque the stepper
      can manage, or I use servo's but there will be others experienced with this
      bit of kit who will help here.

      Regs Mark

      Dr. Mark Vaughan Ph'D., B.Eng. M0VAU

      Managing Director

      Vaughan Industries Ltd., reg in UK no 2561068

      Water Care Technology Ltd, reg in UK no 4129351

      Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH UK.

      Phone/Fax 44 (0) 1872 561288

      RSGB DRM111 (Cornwall)

      From: mach1mach2cnc@yahoogroups.com <mailto:mach1mach2cnc%40yahoogroups.com>
      [mailto:mach1mach2cnc@yahoogroups.com
      <mailto:mach1mach2cnc%40yahoogroups.com> ]
      On Behalf Of Farris Precision
      Sent: 31 May 2010 21:34
      To: mach1mach2cnc@yahoogroups.com <mailto:mach1mach2cnc%40yahoogroups.com>
      Subject: [mach1mach2cnc] missed steps and closed loop stepper controls

      Hello Group,

      I'm new to CNC controls and I'm in the process of researching and building
      my own CNC grinder but I'm worried about missed steps if the load is too
      high on occasion or unforeseen for some reason. I want to learn more about
      missed steps and what happens when the axis motor is loaded beyond its
      ability to overcome the load.

      Is there a way to input data from a linear encoder on the status of output
      movement to be read by Mach3 such that a closed loop system could capture
      missed steps if they occurred. What I'm really trying to get at with this
      question is if something goes wrong and the axis doesn't travel as far as
      you requested (missed steps), is there a way using linear encoders that the
      system can know it needs to continue to move until it reaches the real
      destination even though the number of steps sent should have been enough to
      get you there?

      If something gets in the way of axis movement and there is no feedback in
      the form of linear or rotary encoders, does the motor just not move and the
      steps just get sent through with no response or output or what?

      Thanks,

      David

      New Farris Precision Logo 25%

      Email: david@... <mailto:david%40farrisprecision.com>
      <mailto:david%40farrisprecision.com>

      web: www.farrisprecision.com

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    • Peter Homann
      Fred, That paper and what you are stating supports my point. With microstepping, the accuracy is about 1/2 step but the resolution can be higher. Cheers, Peter
      Message 40 of 40 , Jun 4, 2010
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        Fred,

        That paper and what you are stating supports my point. With microstepping, the
        accuracy is about 1/2 step but the resolution can be higher.

        Cheers,

        Peter

        imserv1 wrote:
        >
        > --- In mach1mach2cnc@yahoogroups.com, "Peter" <groups@...> wrote:
        >>
        >>
        >> --- In mach1mach2cnc@yahoogroups.com, "imserv1" <imserv@> wrote:
        >> ( myth 1 - Microstepping does not improve positioning resolution)
        >>
        >>
        >> Fred,
        >>
        >> Its not a myth. Microstepping increased the resolution. What microstepping doesn't do is increase the accuracy (which is probably what you were trying to say). They are two separate things.
        >
        > Peter, I said what I meant. Aside from the reference to "empty resolution" (from another post) for microstepping granularity over 10 microsteps, I provide you with this quote from the Microchip stepping motor fundamentals paper, which you can reference at this link:
        >
        > http://www.cs.uiowa.edu/~jones/step/an907a.pdf
        >
        > "The dead zone has an impact on microstepping because
        > it limits the angular resolution of the stepping motor."
        >
        > If you look at the graph it shows that it limits it to about 1/2 step.
        >
        > That concept is the basis for my statement about stepper resolution ( which you clipped in your quote, perhaps you missed that part ):
        >
        > Steppers- 400 available physical, under load positions per rev
        >
        > To give you an analogy, saying that 10x microstepping increases the resolution of a stepper motor, compared to 1/2 stepping, is like saying that you have a television screen with 100 dots per inch resolution, until you turn it on, and the display shows only the 5th and the 10th dots out of every 10.
        >
        >
        > Fred Smith - IMService
        > http://www.imsrv.com
        >
        >
        >
        > ------------------------------------
        >
        > www.machsupport.com - Web site AccessYahoo! Groups Links
        >
        >
        >
        >

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