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  1. #1
    Registered
    Join Date
    Nov 2011
    Posts
    9

    NEED HELP with DELTA servo motors

    My old CNC machine broke and I need to replace motors and drives.
    Can anyone help me with setting up new servo delta motors A2 series 400W and 700W closed loop? I need complete help with setting it up.
    I am willing to pay for your help. I was thinking using UCCNC AND UC300, but someone recommended me FATEK FBS 40.
    Please let me know how to finish my job. As I said I definitely can pay you for it
    If you have better ideas, I am open to it. I just need really precise cnc machine.

  2. #2
    Member
    Join Date
    Jan 2005
    Posts
    12178

    Re: NEED HELP with DELTA servo motors

    Quote Originally Posted by tsamael View Post
    My old CNC machine broke and I need to replace motors and drives.
    Can anyone help me with setting up new servo delta motors A2 series 400W and 700W closed loop? I need complete help with setting it up.
    I am willing to pay for your help. I was thinking using UCCNC AND UC300, but someone recommended me FATEK FBS 40.
    Please let me know how to finish my job. As I said I definitely can pay you for it
    If you have better ideas, I am open to it. I just need really precise cnc machine.
    The FATEK FBS 40. is just a PLC I'm not sure why you would need that , you still need the CNC Control and depending on what you need to control most controls will have enough input and output for a normal 3 axis machine
    Mactec54

  3. #3
    Registered
    Join Date
    Nov 2013
    Posts
    1109

    Re: NEED HELP with DELTA servo motors

    Hi,
    I use Delta B2 series servos, and they are pretty straight forward.

    They have a rotary encoder (160,000cpr) like all modern AC servos and the drive 'closes the loop' on that encoder. This allows very high precision angular position
    control.

    The A2 series has a rotary encoder (1,280,000 cpr) about which the loop can close but also a secondary encoder channel about which it can be closed, a linear scale
    for instance. When you say 'closed loop' do you mean 'closed using the built in encoder' or do you mean 'closed around a secondary encoder eg a glass linear scale'?

    If you have ballscrews with backlash, or rotationally inaccurate ballscrews or moderate flex in your machine then using linear scales might be necessary or desirable.
    If however you use pre-loaded ballscrews of at least C7 grade, or C5 grade preferred, then linear scales are likely to add little to you overall accuracy, and 'closing around
    a linear scale' is a redundant luxury.

    I'm going to assume that you mean 'closed loop' around the built in rotary encoder..... then after setting the servo drive up it behaves just like an open loop stepper, your
    CNC motion controller, eg a UC300, issues pulse and the servo moves. The servo drive takes responsibility to get the servo to the desired location in the correct manner,
    and only if it fails in this task (called 'following error) will it cause an alarm. The whole point of using an AC servo like an A2 is to use the smart stuff built into the drive,
    ie the 'closed loop' part. Thereafter using the servo becomes much simpler as the motion controller is relieved of that responsibility.

    There is a figure of merit that will often determine how difficult a servo will be to tune. Its called the inertia ratio. The ratio is that total effective rotational inertia of the
    ballscrew and associated linear axis mass compared to the rotational inertia of the armature of the servo.

    In years past if the inertia ratio was greater than about 5:1 then you were likely to have to do some serious tuning. More modern servos tolerate about 10:1 without
    much in the way of tuning, just the auto-tune feature built in. I would expect the A2 to be of this standard. The B3 series are now touted as being able to accommdate
    ratios of 18:1 without tuning, and I believe the latest model Yaskawa's are even better again.

    In short modern servo drives are becoming so smart which makes them easier to use them....not harder.

    For example, my new build mill has a worst case inertia ratio of 5.5:1. I set the servo up, namely electronic gearing, max accels and velocities, and let rip. I have G0 rapids
    of 25m/min and max G1's of 15m/min with 115kg axis mass with no special tuning at all. I am still experimenting with closing the 'following error window' and 'zero error window'
    down to practical figures.

    I've encountered steppers which take more messing around with than these servos. I love them.

    Craig

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