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IndustryArena Forum > CNC Electronics > Servo Motors / Drives > Yaskawa Sigma-7 10.6kHz Noise, EMI
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  1. #1
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    Question Yaskawa Sigma-7 10.6kHz Noise, EMI

    I have a pair of Yaskawa SGD7S-1R6A00A002 drives, SGM7A-02A7A21 motors (Sigma 7 series, 200W). At the moment I am bench testing a new setup, checking control-board to drive setup. The problem I am having is that as soon as the servo motor is enabled, the drives are emitting extremely annoying audible noise, at ~10.6kHz, and additionally creating substantial EMI, such that surrounding equipment (control board, laptop) functions poorly, if at all.

    Details:
    - The problem is only when the servo motor is enabled. Servodrive on, but motor not enabled there's no issue.
    - If the servo is enabled but the motor isn't plugged in (drive doesn't seem to know this as long as encoder is hooked up), there's no noise or feedback.
    - The motor power wiring is to spec, as far as I can tell (4-conductor 20AWG wire, shielded. Motor grounded, wire shield grounded).
    - Motor power wiring is as short as I can make it (about 75cm). Originally was wired to my whole spool, ~4meters; reducing to 75cm seemed to make no difference.
    - No tuning parameters seem to have any effect on this. The highest I can even set a notch filter is 5kHz.
    - Motors seem to move fine, no noise/vibration. Movement or load have no discernable impact on the audible or EMI noise.
    - Both drives do this, both motors do this.
    - Drives are powered by 230V single phase, provided by step-up transformer from 115V mains (230V single phase is allowed for these drives, and the parameter for it has been set)
    - I acquired both drives and motors used. Claimed to be off working machines, do seem to be in good shape.

    Really hoping someone here can point me in the right direction with this issue! This is my first foray into servos, so I'll take no offense to any suggestion; there's every possibility that I've overlooked something basic. However I'm beginning to worry that this is just the way it is with these drives, which would render them very expensive, unusable hunks of metal.

  2. #2
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    Apr 2024
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    Did you find the cause for this? I have the exact same problem. Used sgmcs 02B and 05B motors and a supposedly new/unused SGD7W-2R8A20A700.

    ~10.5 kHz noise only when motors are active. It is very annoying indeed.

  3. #3
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Nope, I have not figured it out, and it is really damping my enthusiasm on otherwise very nice gear.

    I did put a better quality line filter on the power line, and that helped dramatically with the EMI issues, but did absolutely nothing for the 10.6kHz whine.

    I've found nothing to improve the audible noise. I have only one theory even, which is that perhaps the Servopack capacitors needs replacement. The Servopacks do track capacitor lifetime, and both are basically at 100%. I find that suspicious in a used pack, so I wonder if someone reset the time on them? However, I'm not willing to break open the pack and replace the capacitors without good reason to believe that that's the issue, and so far I've found nothing to elevate this beyond pure speculation. If your packs are new and still making the noise, that seems to be a point against this theory.

    Since I will have water available to the machine already, I'm considering bolting the packs to a coldplate and putting them in a soundproofed enclosure. It feels ridiculous, but I don't see any other way to stand being in the room with them for any period of time without ear protection. And to think, one of the major reasons I went to servos was to avoid the noise of steppers.

  4. #4
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,
    I reckon you are going up the garden path.

    I suspect the servos are dithering.

    Lets say the commanded position is 123456 but the actual position (encoder) is 123457. The servo will try to drive that one step backwards, but it overshoots to 123455,
    so now it tries to drives forward and overshoots to 123457....and so on. and it will dither back and forth at a high frequency and yet by so little amount you cannot detect
    any movement, ie dither.

    Most servos have a parameter that defines a 'Zero Error Widow', that is a parameter usually in encoder counts that if the servo is within the window, ie within a few counts, it will stop
    trying to get even closer. It prevents dither. You'll have to read the manual and find the parameter in Yaskawa's terminology that means the same thing and try widening that window.

    Another possibility is to reduce the integral gain a little and probably also the differential gain by about the same percentage. It could be the the servo is oscillating, again by such a small
    amount you cannot detect movement, but none the less its oscillating. Excessive integral gain will do that.

    Craig

  5. #5
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Interesting; that is not something that it ever would have occurred to me could happen at such high frequencies. Pretty impressive, actually.

    Appreciate the suggestion, Craig! I'll take a look at this when I have the chance to hook up the laptop and tuning software. Fingers crossed.

  6. #6
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    I have increased the error window to the point of significant slop before the servo tries to correct, and gains down so low the servo would be unusable. Neither had any effect on the 10.6khz noise.

    I will again note that movement or load have no discernable impact on the noise. While I still don't claim any expertise in servos, I don't see how dithering or oscillation noise wouldn't be reactive in some way to what the servo is doing?

  7. #7
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    What's the bandwidth of the servo drive control loop?

    I would guess if it was dithering causing the noise, the bandwidth would have to be equal or higher than the sound frequency??
    I could be completely wrong.

    Most servos don't have 10kHz control loop bandwidth.
    Delta servos are 2.5-3.1kHz (current generation, depending on model).
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  8. #8
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    They are 3.1kHz response frequency.

    I have been thinking along the same lines; I don't see how they could dither faster than 3.1kHz as an absolute theoretical maximum. Since they are AC, maybe that could explain noise up to 6.2kHz? Either way, 10.6kHz is hard to explain for me.

    I continue to lean towards this not being a tuning issue, but either a normal intrinsic property of the drives (would love for someone to be able to confirm or deny this), or possibly an issue with past-lifetime capacitors.

  9. #9
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,
    the cycle time may be 3.1kHz, that is to say the PWM gets calculated afresh at 3.1kHz, but the PWM tick rate is much MUCH faster than that, more likely 20kHz.

    I continue to lean towards this not being a tuning issue, but either a normal intrinsic property of the drives (would love for someone to be able to confirm or deny this), or possibly an issue with past-lifetime capacitors.
    I am coming to the same conclusion, that it seems less like a dither issue, nit that I discount it completely, but rather like you that it is something else. I do not suspect faulty capacitors. How and why would they make a noise?
    Are they subjected to currents of 10kHz?

    Craig

  10. #10
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Quote Originally Posted by joeavaerage View Post
    the cycle time may be 3.1kHz, that is to say the PWM gets calculated afresh at 3.1kHz, but the PWM tick rate is much MUCH faster than that, more likely 20kHz.
    Ok, I see; so the "decision making" is happening at 3.1kHz, but actual motor-drive signal is chopped much finer than that? That makes some sense.

    I admit the capacitor theory is entirely a shot in the dark, prompted only by the facts that I find the 100% remaining capacitor lifetime in a used drive suspicious, combined with my possibly erroneous prior belief that aging capacitors can cause whine/squeal noise in a circuit. I am quite happy to set that theory aside in pursuit of more likely culprits.

    On the basis of solid facts, I have no particular reason to expect any specific components to be subjected to frequencies in the 10.5kHz range; I cannot find anything in the manuals that talks about anything around these frequencies. All tuning references to notch filters, oscillations, etc., top out well below this. I can find no troubleshooting references anywhere regarding acoustic noise generation above vibration/oscillation ranges up to about 1000Hz.

    I appreciate the help, and would gladly take any suggestions on what to investigate next.

  11. #11
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    Apr 2024
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    I also had no luck when increasing the Pn522 - Positioning completed width.

    In my case, both the servos and the Servopack make the same frequency noise ~10.7khz. I have been in contact with Yaskawa support and sadly they say that this noise is normal when the servos are on.

    I also sent a video of my setup to support. This is the reply:

    The noise from the servopack is due to SERVO ON, this will always cause some noise. Regarding the servo motor, it seems normal, especially since you are attempting to move the motor while it is energized (magnetized). This noise arises because the servo is actively working to maintain its position and counteract any displacement.

  12. #12
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,

    This noise arises because the servo is actively working to maintain its position and counteract any displacement.
    That is almost exactly what I said from the beginning.

    I suspect the PWM output of the servo drive is 10.7kHz, or maybe some multiple of it. The cycle rate of the control loop has nothing to do with the PWM rate. I rather suspect the noise you are hearing
    is not 'dither' but rather is one of the audible harmonics of the PWM.

    How long are the cables between the drive and the servo?

    There is in most manufacturers specs, Yaskawa included, that call for motor side (called load side) reactors if the cable length is long. May I suggest you consider trying load side reactors.
    You need to be exceptionally careful here. Most EMI line filters have capacitive input and capacitive input filters are VERBOTEN with PWM output devices. The load side reactor input impedance
    MUST be NET INDUCTIVE or you risk your drive.

    With the forgoing, then ordinary EMI filters CANNOT be used on the load side of a servo drive. If you are going to try load side reactors then I would follow Yaskawa's instruction carefully.

    Line side reactors and EMI filters are very much easier to find and specify.....and any capacitive input of an EMI filter will do no harm on the line side, but not so on the load side.

    Craig

  13. #13
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Quote Originally Posted by EinarH View Post
    The noise from the servopack is due to SERVO ON, this will always cause some noise.
    Seems they could have just stopped here. It makes absolutely no difference if you are trying to move the motor, no difference if you are introducing any perturbations at all; the noise is simply there when the servo is on.

    My motor wiring is only about 75cm long, and the reactor Yaskawa calls out doesn't seem to be easily found online anyhow, so not sure it worth messing with that for me.

    Looks like I will be moving forward with the cold-plate acoustic box.

    Bad news, but thanks everyone for the help. At least I can move forward with more confidence.

  14. #14
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    OMG I found something!

    Change Pn009.1 "Current control Mode Selection" to "2: Use current control mode 2".

    Now my motors (and drive) only make noise when they are MOVING. When they are ON, but not moving, the 10.7 kHz noise is gone. Amazing.

    The manual says:

    Current control mode selection reduces high-frequency noise while the Servomotor is being stopped.
    To use current control mode selection, use current control mode 2 (set Pn009 to n.??2?).

    BTW, what line filter did you use? I also have EMI issues.

  15. #15
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,

    This is the sort of thing you'd put on the input (line) side of your drive:

    https://nz.element14.com/corcom-te-c...ase/dp/9586474

    Note that this is a two stage filter, if you are going to the trouble and expenses of fitting EMI filters you should make them all two stage verses single stage.

    It is also a good idea to put one on the input side of any sensitive stuff, like the PC and controller. The one at the input of the drive is to try to 'contain' the EMI within the drive, while the one at the input
    to the PC is trying to 'exclude' EMI from entering the PC.

  16. #16
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,
    VFDs and servo drives generate a lot of switching harmonics which can 'pollute' the local supply, those harmonics can enter other sensitive equipment and cause issues. EMI filters are poor at rejecting this
    kind of harmonic. If you have real trouble then fit a line reactor.

    As an example, this is for a three phase drive:

    https://nz.element14.com/corcom-te-c...line%20reactor

    Whereas this is for a single phase drive:

    https://nz.element14.com/corcom-te-c...line%20reactor

    They greatly reduce harmonics and very much improve power factor, and will reduce nuisance circuit breaker trips if you have a marginal or C curve breaker.

    Can be had second hand on Ebay.

    The only pesky and persistent noise issue I've ever really had was when I was pushing my little 1hp VFD hard. I tried many things until I fitted a reactor....and thereafter never another problem.

    Very big VFD's, say 100kW and more, having a line reactor or some other active power factor correction is mandatory....or the power company will be on your case with the harmonics doing bad things
    to their network equipment.

    Craig

  17. #17
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Thanks alot for the suggestions! I bought this:https://docs.rs-online.com/b069/0900766b81216c49.pdf (two stage). Way more current than I need, but I want it quick, and this was in stock.
    It is also "Designed for frequency inverters and variable speed motor drives", which is good, I hope.

    Would you just throw in a line reactor on top of this just for good measure, or is it a thing you wire up if you really need it? My setup has two DDR servos, one 42W and one 105W.

  18. #18
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,
    I personally am in favour of line reactors as a matter of course, but the vast majority of CNCers do not do so, without apparent harm....unless you consider EMI and nuisance trips 'harm'.

    Your choice.

    Craig

  19. #19
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Quote Originally Posted by EinarH View Post
    OMG I found something!

    Change Pn009.1 "Current control Mode Selection" to "2: Use current control mode 2".

    Now my motors (and drive) only make noise when they are MOVING. When they are ON, but not moving, the 10.7 kHz noise is gone. Amazing.

    The manual says:

    Current control mode selection reduces high-frequency noise while the Servomotor is being stopped.
    To use current control mode selection, use current control mode 2 (set Pn009 to n.??2?).

    BTW, what line filter did you use? I also have EMI issues.
    Interesting find, EinarH. This may be a nice fix in some scenarios. Unfortunately, they will also make noise when they are loaded/resisting, and it also seems to be easier to knock them out of position in this mode. And finally, this mode is not intended for the smaller drives like mine, so while I did play around with it a little bit, I don't won't run it long term.

    The line filter I changed to is a TDK-Lambda 285-2626-ND. I don't remember what my previous one was, but it was something cheapo, and the difference going from it to this one was night and day. It is a two stage, but with an additional resistor/capacitor stage compared to the Corcom one you linked.

  20. #20
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    Re: Yaskawa Sigma-7 10.6kHz Noise, EMI

    Hi,
    the apparent 'additional' resistor/capacitor is not relevant. Two stage means there are two inducive elements and two capacitive elements in the transfer function. In practice the two elements,
    both inductors and capacitors, may be realised as more than two each, but the all important transfer function is still two stage, or technically 'four pole Chebyshev' or possibly 'four pole Butterworth', maybe even 'four pole elliptic'
    If your line filter has a genuine 'extra capacitor' then it would be 'five pole Chebyshev or 'five pole Butterworth' etc', and therefore better....and you would know by virtue of cost.

    Craig

    PS: Comes from a lovely piece of theoretical work (Fosters Reactance Theorem) published in 1924 by Ron Foster....I remember it well...it was a Tuesday!!!

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