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Thread: Auto tuning

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  1. #1
    Join Date
    Apr 2015
    Posts
    6

    Question Auto tuning

    Hi,
    I have no experience with servos. Should I pay extra for servos that have auto tuning capabilities or is ti ok to buy ones that have to be tuned manually and then tune them myself?

  2. #2
    Join Date
    Jun 2005
    Posts
    1723

    Re: Auto tuning

    It is much easier to get a nicely tuned machine with servos and amps that have auto tuning. Manually tuning these systems is not easy

  3. #3
    Join Date
    Nov 2013
    Posts
    4280

    Re: Auto tuning

    Hi,
    I agree, if you are new to servos then Auto-tuning is a Godsend.

    Funnily enough its not even so much the Auto Tune feature but the fact that you have software on a PC that you can program and eventually tune the servo
    that is the real Godsend. A lot of cheap Chinese servos have no such software and so you have to program them by pushing buttons like a microwave.
    There are hundreds of parameters....so you really don't want to do it that way, its just too error prone and the Chinese manuals are typically useless.

    If however you buy a better standard of servo, I use Delta for example, Taiwanese made in China, but has set-up and tuning software including Auto Tune.

    There is a parameter, a 'figure of merit' that will tell you how hard it will be to tune a servo. Its the inertia ratio. The first moment of inertia of the servo
    is published by the manufacturer. The first moment of inertia of the ballscrew, couplers and the weight of the axis all needs to be calculated, and the ratio compared.

    For example my new mill has 750W Delta servos with J=1.16 x10-4 kg.m2

    The ballscrew and 150kg axis (5mm pitch screw) has J=9.3 x 10-4kg.m2

    So the ratio is 9.3/1.16 = 8

    So the inertia of the ballscrew and axis is 8 times the inertia of the servo. This is in the sweet spot for Auto Tune. Auto Tune works really well from about 3 to 10.
    After 10 it starts to look a bit challenged. Its a good place to start but you'll probably want to tweak it a little even after Auto Tune. Beyond about 15 Auto Tune
    start looking pretty dodgy...but with care and use of notch filters and other aids you can tune out to 25.

    If you have a regular machine with an inertia ratio in the range of 3 to 10 then Auto Tune is great.

    Craig

  4. #4
    Join Date
    Apr 2015
    Posts
    6

    Re: Auto tuning

    So one could say that when I make sure the servo manufacturer/seller can provide English-translated software that it will be ok for me to tune the servos myself?

    I mean this isn't a complex machine we are talking about. It's just a servo>gearbox>rack&pinion setup.

  5. #5
    Join Date
    Nov 2013
    Posts
    4280

    Re: Auto tuning

    Hi,
    have you set up a servo before? If you have not, I'd strongly recommend a model or bran that has set-up software as a minimum and tuning software including Auto Tune
    suggested.

    There is a reason cheap Chinese servo are cheap.

    Craig

  6. #6
    Join Date
    Jan 2013
    Posts
    474
    Quote Originally Posted by Redi View Post
    Hi,
    I have no experience with servos. Should I pay extra for servos that have auto tuning capabilities or is it ok to buy ones that have to be tuned manually and then tune them myself?

    I mean it's 600 bucks total for drivers that support tuning over drivers that don't.
    The only servos I'm familiar with that auto tune are those with high speed motor spindles. To teach in, they accelerate through their ranges up and down using built in system software and scope function.

    If you are talking about axis motors, usually the standard setting parameters by application are needed.

    So, unless you are fine tuning a spindle to achieve optimum performance, I would manually tune.

  7. #7
    Join Date
    Nov 2013
    Posts
    4280

    Re: Auto tuning

    Hi,
    you'll find plenty of posts both on this forum and others where newcomers (to servos at least) have bought cheap Chinese servos and very much struggled to set them up
    and tune them in absence of manufacturer supplied software. Its not that its impossible, and if you have some experience already perfect doable....but if you don't
    have that experience to draw on I would suggest the setup and tuning software is required. Your call.

    I recognise that it costs extra.

    I buy 750w Delta B2 servos for $438 USD plus shipping each. From the same supplier they sell a ToAuto brand, and a 750W servo kit costs $292USD. I still pay the extra, not really because of
    quality concerns, although I do believe Delta better in that regard, but mainly because of setup software. I have on my PC now several setups that I have used on my machine and others.
    When I program a new servo I just grab one of those saved setups and copy and paste, 30 seconds work to set up a new servo. Too easy. You'll not do that with the cheaper servos.

    Its your money and your call.

    Craig

  8. #8
    Join Date
    Dec 2013
    Posts
    26

    Re: Auto tuning

    Hi Joe what you do if you have those chinese serve and want to tune up . My machine is running but my two motor on y are making my gantry a kind of parkinson shake , it going be kind of step that tremble my gantry . I'm in the fog zone , no one to call and see nothing .
    What to do?

  9. #9
    Join Date
    Nov 2013
    Posts
    4280

    Re: Auto tuning

    Hi,
    both servos must be tuned to be perfectly in synch with each other.

    I would try disconnecting one servo, if possible, and tune the master servo. Once you've got the master tuned then apply all those parameters, to the last detail,
    to the slave servo.

    Do these servos have any software? If they do then you can save the parameter settings of one servo and clone another. I have done so using Delta servo software,
    it's way convenient.

    Craig

  10. #10
    Join Date
    Dec 2013
    Posts
    26

    Re: Auto tuning

    Thanks Craig for the fast reply , My question was more about what variable I should work with .My shaking is in when my machine is changing of side ,look the video . There 0.003 " back lash on that axe. on strait line on problem.
    What would append if I'm changing value in Pn 113 to pn 116 . I think at something , at what kind of control PN002 the servo should be set at first , that mybey why is give problem ( now is set to #2 location mode ) . I'm so far from home here , can you help.
    thanks
    Alain

    https://drive.google.com/file/d/1iiz...ew?usp=sharing

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