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  1. #1
    Join Date
    Dec 2007
    Location
    Adelaide
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    465

    Default Question for the stepper motor experts

    Looking at stepper motor drivers I see that micro-stepping can be set from 200 up to 40,000 steps for 1 revolution of the stepper, one would have to assume that increasing the number of steps per rev would increase positional accuracy, I have also read that it can make stepper operation smoother, but there has to be a limit where a trade off situation is reached where speed, torque or some other aspects of the performance start to suffer. A small table below shows the effect of steps per rev on accuracy for given an arbitary axis move of 15.53mm (not real high precision), assuming a standard 5mm pitch ballscrew. In each case the number of steps needed to move that distance (15.53mm) is not an exact number but includes a partial step which is of course in the real world is not possible, the actual distance moved is given to 4 dec points


    Micro step --------------------------------------Actual distance the axis moves.
    200----------------------------------------------------------15.525
    800 ---------------------------------------------------------15.525
    1600--------------------------------------------------------15.5281
    3200--------------------------------------------------------15.5296
    6400--------------------------------------------------------15.5296
    12800-------------------------------------------------------15.5296
    25600-------------------------------------------------------15.5298


    What is the practical limit for microstepping - from the table it looks as if it is not worth going beyond 3200 or even 1600 micro steps per rev
    Screenshot 2022-09-09 002415.jpg

  2. #2
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    5,579

    Default

    Hi FamilyGuy,

    Realistically there is very little to be gained going higher than 800 steps ! Apart from increasing motor heating, there is more chance of missing steps.

    Basically each time you divide a step you increase the pulse rate, so half a step will have two pulses, a quarter step will have four and so on. Depending upon the stepper you get to the point where the motor becomes unable to keep up and the load on the stepper will increase this effect, resulting in missing steps.

    This is also why servo feedback systems are preferred for high precision systems.
    Best Regards:
    Baron J.

  3. #3
    Join Date
    Apr 2019
    Location
    Adelaide
    Posts
    459

    Default

    You could always make your system closed loop by installing a rotary encoder to assist with accuracy.

  4. #4
    Join Date
    Sep 2009
    Location
    Newcastle
    Posts
    299

    Default

    Microsteps are for smoothness. They are not reliably accurate.

    There are some explanations of the electrickery psychics available via your nearest search engine that are better than I can provide.

  5. #5
    Join Date
    Dec 2007
    Location
    Adelaide
    Posts
    465

    Default

    There is a lot of web sites explaining the pros and cons of microstepping, none seem to give definitive answers and none seem to mention microstepping of closed loop steppers, which is what I have. I've currently got my microstepping set at 1600 steps per revolution, which I don't think is aggressive, I guess the only way to really tell is to do some real world testing which I'll get around to, while changing the microstepping is easy enough, last time I changed from 800 to 1600 steps per rev I didn't realise that I probably should have moved the X and Y axis to the 0,0 origin point first, so after flipping the switches on the stepper driver I found that not only was my 0,0 origin point somewhere in the middle of the table, my soft limits were also out, so I had to go through the process to reset both.

  6. #6
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
    Posts
    5,579

    Default

    Hi FamilyGuy,

    Just in case its not obvious, a two pole 1.8 degree (200 steps) stepper requires 400 Hz for one rotation per second. Or 1.4 Khz at 800 microsteps.
    Best Regards:
    Baron J.

  7. #7
    Join Date
    Dec 2007
    Location
    Adelaide
    Posts
    465

    Default

    I set my steps per rev to 3200 for both X and Y axis, and used a part I need for a project as a test. A 70mmx30mmx25mm block of steel, cut from a larger piece - not sure of the composition but I think it is some sort of tool steel - if I'm a bit slack drilling holes in it, it does work harden. I wanted 2 holes through the 30mm section, 1x10mm diam and the other 15mm diam, the 10mm hole had to be right on10mm to take a 10mm rod for a neat sliding fit - I don't have a 15mm drill or a 10mm reamer.


    To give the metal chips a better chance to clear, I pre-drilled the holes 6mm and 10mm the idea being that chips would fall through rather than be caught up in the bottom of a narrow pocket as I approached the 30mm depth. The 10mm hole was bored with a 7mm HSS 4 flute cutter around 2500rpm 120mm/min feed with 4 stepovers and a 0.25mm finishing cut, the 15mm hole as bored with a 12.7mm HSS 4 flute cutter around 2000rpm and the same 4 stepovers and 0.25mm finishing cut. The 10mm hole came out perfect the 10mm rod was a nice push fit which I thought was good considering I didn't compensate for cutter/runout (I know my ER chuck has a bit of runout) - while the 15mm hole was not that critical as it was only to take a 16mmx1mm thread I did take the time to measure with an expanding bore gauge 14.994mm as measured with my digital mic, I know that there is a knack to using expanding bore gauges when it comes to consistent results so my measurement does have an unknown plus or minus tolerance, but as the only other way for me to get a 15mm hole would have been to bore it on the lathe and I know I couldn't do any better than the results I achieved.

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