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IndustryArena Forum > CNC Electronics > SmoothStepper Motion Control > Missing Z steps on a 3d toolpath
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  1. #1
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    Missing Z steps on a 3d toolpath

    Hi All,
    Im wondering if you could help me with an issue I run into lately on my first complicated 3d toolpath.
    Recently I build a PrintNC CNC machine. Its running Mach4 with an ESS.
    I noticed on 3d toolpaths I seem to be missing steps. The only solution so far is reducing the acceleration to less than 40mm/sec2, I feel this is way too slow for what the machine should be able to do, am I wrong?.
    Since the gcode I'm running has many small movements, I made some test code and sound some resonance at lower speeds which I cant get rid of. Fast accelerations > 1000 are fine and lose no steps.
    Here are some videos to show what I'm talking about.
    https://youtu.be/oq0QyY60Eic
    https://youtu.be/37ibDpoQdHM

    Any input would be appreciated.

    notes.
    drivers are DM542 @ 36V
    Mechanicals have been checked, no slippage.
    Tried 1/2 to 1/125 microstep, same result.
    Tried different currents.
    Tried different stepper.
    Tried different driver.
    increased look ahead.
    changed operating frequency - went really bad then!

  2. #2
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    Re: Missing Z steps on a 3d toolpath

    Hi,
    36V is a joke, you need a lot more than that.
    What is the inductance of the steppers?

    Craig

  3. #3
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    Re: Missing Z steps on a 3d toolpath

    +1 with Craig.
    Your supply prob can't cope.
    If steppers are more then 3mh inductance then ditch the DM542 in favour of some DM860 and run on 60V.
    (48V on the 542 is a bit close to max).
    I swapped out and haven't found a fail point on accelleration. I've had it up to 3000!. Left it on a 1000 setting and lowered driver current to next setting down.

    Higher voltage = higher speeds. Just have to adjust amp current settings according to motor heat.

  4. #4
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    Re: Missing Z steps on a 3d toolpath

    Hi,
    They are 57HS100-4204 so I believe they are 3mH.
    I have a 48V supply I can test on, maybe that's the next option.
    I really cant understand this. Every test I perform has a different outcome and I'm close to throwing this in the bin and buying a closed loop stepper system, however I think there is an underlying issue here which maybe compounded by closing a loop. It might just complicate things in the future.

  5. #5
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    Re: Missing Z steps on a 3d toolpath

    And regarding the power supply. The thing runs fine running simple 2.5d toolpaths. Only running 3d have I seen an issue. All testing at the moment has the X & Y steppers disconnected, so all 300W of power supply is available for one stepper, and remember its only losing steps at very little loading.

  6. #6
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    Re: Missing Z steps on a 3d toolpath

    Hi,
    closed loop steppers are still steppers and suffer the degrading torque the faster they go. The manufacturers of the closed loop steppers would have you you believe
    they never miss steps, go faster, more powerful......yada yada yada.....all pure BS.

    A stepper, whether it be open loop or otherwise will only ever miss a step if its OVERLOADED AT THE SPEED OF OPERATION. A closed loop stepper will recognise that a step has been missed
    and insert an extra step, but guess what.....that step is just as likely to be missed as a regular step because the stepper is OVERLOADED AT THE SPEED OF OPERATION. If it misses too many
    steps it will fault out and stop, producing an alarm signal to the controller.

    The one advantage over open loop steppers is that they can successfully interpolate between steps up to the resolution of the encoder, but you have paid dearly for that
    modest gain.

    If you really want closed loop performance then pay up for AC servos, they EAT steppers....but are not cheap. Even the cheapest Chinese ones are nearly double the price of a good stepper
    and stepper drive.

    If you cant get open loop stepper to run properly you wont get closed loop[ steppers going any better. Save your money for things that actually make a positive difference.

    All steppers lose torque the faster they go. Inductance is a good measure of how bad that torque degradation will be, the lower the inductance the better. A stepper of 5mH inductance
    with a decent driver will have only about 5-10% of its torque at 1000rpm....yes thats right less than 10%. A stepper with low, say 1mH inductance may well have 40-45% of its torque
    at 1000 rpm with the same driver.

    Your 3mH steppers are not the worst out there, but neither are the the best. I always recommend for 23 size steppers: 1-2mH, 1mH preferred and reject anything over 2mH.

    The classic way to overcome inductance is by using higher voltage drivers, the higher the better. At the current time 80VDC is highest voltage of readily available drivers at reasonable prices.
    I would recommend you get some 80VDC drivers and an 80VDC power supply. The higher voltage may be enough to persuade your existing steppers to go fast enough. If not then
    you might be looking for new LOW INDUCTANCE steppers.

    You'll never regret buying high voltage drivers and supply....if you buy good quality you'll have them for twenty years.

    Craig

  7. #7
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    Re: Missing Z steps on a 3d toolpath

    Hi,
    stepper motors, like any motor, generates current back into its drive/supply on deceleration. If there is ever a time a driver or supply will blow up it's when the
    motor is decelerating.

    When buying a power supply I would recommend a linear supply, that is one with a transformer, rectifier and filter capacitors, rather than switch mode supplies.
    Switch mode supplies, especially at high outputs are cheaper but are much more likely to go BANG than a linear supply.

    This is a good example:
    https://www.antekinc.com/ps-10n80-10...-power-supply/

    Gecko stepper drives have a great reputation for reliability and performance but aren't cheap, howvere there are plenty of perfectly good Chinese made drives
    at much sharper prices, this is an example:
    https://www.ebay.com/itm/17481010498...Cclp%3A2334524

    Craig

  8. #8
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    Re: Missing Z steps on a 3d toolpath

    Thanks for everyone's input.
    There are two directions I can go here and both will cost quite a bit of money, so I just want to be sure I don't spend twice.
    Ideally I would upgrade my SMPS and stepper drivers and all problems may go away, however I'm not sold on this yet and this is why.
    I connected a smaller 23hs22-2804S to the setup on the Z axis and didn't connect any mechanicals, this stepper is 2.5mH inductance.
    I ran the same test and still have the same "free air" step loss.
    This is at 40mm^2 acceleration.
    My scrip moves 0.01 back and forth, I'm not pushing any speed barriers here.
    Do you still think voltage is my issue?

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