Problem with Y axis, need help!!


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    Default Problem with Y axis, need help!!

    Hi Guys, I was working on my mill today and just after starting a job i thought i heard the Y axis make a bit of a rumbling noise but couldn't say for sure as i had ear plugs in. Everything seemed fine again and then a few minutes later after drilling and tapping about 30 holes, it toolchanged to a different tap and proceeded to try and tap a hole nearly 1/4" off center. So it broke the tap and messed up the part and obviously now i have some kind of feedback problem.

    After this, I made some rapid moves in the Y axis, moving a few inches and then back to zero again and it seems fine at low rapids, but when you increase speed it sounds rough and loosing position slightly. I didnt do too much testing here as i was very fearful of a runaway. So initially i'm thinking this sounds like a loose encoder coupling or bad encoder, but I've checked coupling and its perfect. I have some spare encoders so i tried a whole new encoder and same problem. I've checked all the connections on the encoder cable, and traced the full length of the cable and everything is perfect. The Y axis cable is stationary and completely free of coolant too so unlikely to cause too much trouble anyway.

    So starting to get a little nervous now. What else could I look for? Could there be an issue with how the pulses are read by Kanalog? Im guessing this is very unlikely. Is it worth my while to try moving the connections to a different encoder input? I do have one spare set of inputs i think. Anything else i can try? Thanks!

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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    If the machine moves to the wrong place and doesn't disable with a following error then the encoder's Position must be incorrect (assuming a reasonably small Max Following Error setting).

    You might use the Step Response Screen at a speed that fails and plot the result. That may provide some clues.

    You might measure the encoder A+ A- B+ B- signals at Kanalog to make sure they are all switching to valid voltage levels and that none of the 4 are floating.

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Sounds more mechanical than electrical.
    Have you checked all the mechanics?
    If it's driven via belt, a stripped belt could cause those symptoms. Even just a loose coupler may cause similar problems, although couplers are more likely just to slip continually.



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    Default Re: Problem with Y axis, need help!!

    A little update guys, got some good news and bad, I powered up the machine again last night and everything is back to normal. Still have the spare encoder on there. So everything is working fine now. But the bad news is I have no idea what caused it and i'm terrified it could happen again any time. I ran a test program again last night with repeated Y axis moves and everything was fine, sounded great at all speeds. And i went ahead and ran 2 more parts with the machine and they cut fine. I did keep the rapids dialed back. The only thing i did different since was look over every inch of the cable again for damage (looks perfect) and I wiggled the green terminal block on the kanalog board, pulled it half way off and pushed back on. Could there possibly be a bad connection between this terminal block and the pins on the board? Anybody ever have any issues with these? Guessing this is very unlikely as well, but i cant think of anything else? Should i replace the entire cable as a precaution? This is a fairly large machine, a runaway at a bad time could cause a lot of damage.

    Tom, yes following error is set at 1500 counts or about 0.012" and it didnt disable so I must have lost position somehow. I will try the step response screen next time, thats a good idea. I measured the voltage across each a/b pair and im getting 3.59 from my X axis, 3.35 from my Y and 3.65 from Z. Interesting that the Y is lower then the others. This is with the replacement spare encoder I have on there. Not sure what the original was. Also noted my spindle encoder at 3.1v and this reads fine. What should i be seeing here? does this sound ok? Do I also need to check to ground?

    Moray, the servos are direct drive with fairly heavy duty couplers between servo and ballscrew. I had a little backlash here before so i went a little overkill and added a second setscrew and loctited everything. They are keyed as well so even if loose I should only be seeing a little extra backlash instead of something like this. Also checked encoder couplings and it is solid.



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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    I assume you measured the encoder voltages across the + and - pins? And those were sometimes positive and sometimes negative? I normally check each pin relative to Kanalog GND that they switch between ~0.4V and ~3.4V providing like 3V differential. The threshold is only like 0.4V.

    I haven't heard of any issues with the connector pins.

    Sounds like most likely the cable. You might put the machine in the air moving Y back and forth and wiggle and pull on the cable to see if you can cause a problem.

    Maybe tighen up the Max Following Error to have a better chance of disabling if it starts to "rumble" again.

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Quote Originally Posted by TomKerekes View Post
    Hi Mark,

    I assume you measured the encoder voltages across the + and - pins? And those were sometimes positive and sometimes negative? I normally check each pin relative to Kanalog GND that they switch between ~0.4V and ~3.4V providing like 3V differential. The threshold is only like 0.4V.
    Hi Tom, Yes that was across positive and negative, i guess some were negative, i didnt really take notice. I just checked voltages to ground and im getting:

    X 3.77, 0.17, 0.17, 3.77

    Y 3.65, 0.27, 0.27, 3.65

    Z 3.79, 0.13, 3.79, 0.13

    So you say the threshold is 0.4 volts? So does this mean im kinda close on the Y axis here? If this is questionable maybe i should switch encoders again and see what the origional was? Possible I have 2 boarderline encoders?

    I haven't heard of any issues with the connector pins.

    Sounds like most likely the cable. You might put the machine in the air moving Y back and forth and wiggle and pull on the cable to see if you can cause a problem.

    Maybe tighen up the Max Following Error to have a better chance of disabling if it starts to "rumble" again.
    Ok good to hear about connectors. I did a repeating program of Y moving and wiggled and pulled at the connectors and all over the cable and nothing showed up. Was starting to gain a little confidence again and was setting up another job and before running it I ran my test program again and "think" i heard the noise again for a second Maybe it was just my mind this time, not exactly sure.

    I will reduce following error, thats a good idea. I wonder how low i can go without nuisance trips? Servo gain is P 2. I 0.025 and max output is 1000. So i guess max output would be at 500 counts ignoring I gain. Would this be a good place to start? Or even less? Thanks.

    Edit: I tried following error of 100, planning to work upwards and it actually runs like this! Machine ran fine for last hour or so. Amazing, thats an error of less then a thou and its able to do rapids at 100% speed and fairly heavy cuts without giving a following error. Hopefully this will catch an error the next time it happens.


    Mark

    Last edited by mmurray70; 10-28-2018 at 08:19 PM.


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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    X 3.77, 0.17, 0.17, 3.77

    Y 3.65, 0.27, 0.27, 3.65

    Z 3.79, 0.13, 3.79, 0.13

    So you say the threshold is 0.4 volts? So does this mean im kinda close on the Y axis here? If this is questionable maybe i should switch encoders again and see what the origional was? Possible I have 2 boarderline encoders?
    That all looks perfectly correct. The difference between the + and - voltages must exceed either +0.2V or -0.2V to switch the output state. In your case of 3.65 - 0.27 = 3.38 far exceeds the necessary +0.2V

    I will reduce following error, thats a good idea. I wonder how low i can go without nuisance trips? Servo gain is P 2. I 0.025 and max output is 1000. So i guess max output would be at 500 counts ignoring I gain. Would this be a good place to start? Or even less?
    You can't really determine the following errors from the gains. The best way is to use the step response screen and do worst case moves and observe the maximum errors, then set a limit a bit higher.

    Regards

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Quote Originally Posted by TomKerekes View Post
    Hi Mark,

    That all looks perfectly correct. The difference between the + and - voltages must exceed either +0.2V or -0.2V to switch the output state. In your case of 3.65 - 0.27 = 3.38 far exceeds the necessary +0.2V
    Ok I understand what your saying now. Great this looks good.

    You can't really determine the following errors from the gains. The best way is to use the step response screen and do worst case moves and observe the maximum errors, then set a limit a bit higher.

    Regards
    See edit in the last post. I tried setting it really low, planning to work my way up to the point where it would run, and its actually running with a following error of just 100 counts or 0.0008". Hopefully this will catch it if it messes up again.

    Also FYI, i tried setting it at 10 just to be sure it would actually disable and it does. But gives me a G-code error message when it happens? I thought back in a previous version it actually said following error exceeded. Not a big deal but just thought i would mention it.



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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    Also FYI, i tried setting it at 10 just to be sure it would actually disable and it does. But gives me a G-code error message when it happens? I thought back in a previous version it actually said following error exceeded. Not a big deal but just thought i would mention it.
    You should see this:

    Problem with Y axis, need help!!-axisdisabled-png

    Do you see something different?

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Yes thats what I got. I guess thats the way its meant to be. Sorry I sort of thought that at some point in the past I got an error that actually said following error exceeded but i guess not.

    Ill keep you guys updated if i have any more trouble with this. Thanks again for the help!



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    Default Re: Problem with Y axis, need help!!

    Hi Guys, unfortunately I had this issue come back again a couple weeks ago. Same problem exactly. Rough sound in Y axis under rapid and then position slightly off. Worked fine for a year and a half and finally showed up again. Working fine again now too. Lately I've been doing some rework on some expensive parts so im a little nervous about the issue popping up again.

    Any suggestions on anything else I can check? Everything mechanical seems good. Encoder was replaced last time I had the problem and didnt change anything. Thinking of making a whole new encoder cable/connector and changing that.

    Would there be any point to move to a different encoder input on Kanalog?



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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    Sorry to hear you are again having problems.

    If the position shifts off the problem must be related to the encoder. Either the encoder itself, the wiring, the interface, or the related hardware/software. With a properly working encoder regardless of what happens, rough motion, crash, or whatever the encoder should still track the position. I suppose one exception is if the motion exceeds the encoder count rate, but I would expect that to be impossible or unlikely.

    Was the offset only in the Y axis?

    Does the Y encoder cable flex at all?

    What max following error are you running with? No following error occurred?

    What was happening before the problem occurred?

    What is the rapid move velocity in counts/sec?

    I think the most likely thing would be an intermittent encoder cable. With one broken wire the encoder could count unreliably.

    I suppose we could write a background task to be recording data and if we could somehow trigger save the data for analysis.

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Quote Originally Posted by TomKerekes View Post
    Hi Mark,

    Sorry to hear you are again having problems.

    If the position shifts off the problem must be related to the encoder. Either the encoder itself, the wiring, the interface, or the related hardware/software. With a properly working encoder regardless of what happens, rough motion, crash, or whatever the encoder should still track the position. I suppose one exception is if the motion exceeds the encoder count rate, but I would expect that to be impossible or unlikely.

    Was the offset only in the Y axis?

    Does the Y encoder cable flex at all?

    What max following error are you running with? No following error occurred?

    What was happening before the problem occurred?

    What is the rapid move velocity in counts/sec?

    I think the most likely thing would be an intermittent encoder cable. With one broken wire the encoder could count unreliably.

    I suppose we could write a background task to be recording data and if we could somehow trigger save the data for analysis.
    Hi Tom,

    I have eliminated the encoder as a possibility. The original encoder I was using ran fine for a year or so, when it acted up the first time (in 2018) I changed to a spare encoder and still had the problem when jogging the machine. I left the spair encoder on the machine and later that day the problem disappeared and its been running fine ever since, until just recently. So im pretty sure both encoders are working fine.

    - Yes the offset was only in Y, never ever have in issue with the other axes.

    - No flex or coolant exposure on the Y axis cable. The others take far more abuse and work fine.

    - I was running a following error of 300 counts. CPI is 121920 so this is 0.0025" and I did not get a following error. I have reduced this to 100 counts (under 0.001") to be more likely to trigger a following error in the future. Should I go lower still? Not sure how low I can go without getting nuisance trips from normal operation, running fine at 100 counts now.

    - Everything was running fine, running a program and noticed a rough sounding Y axis rapid move. Stopped the machine and noticed position was out. When this happend in 2018 it was in middle of a program tapping holes. Tapped the first few fine, made a rough sounding move and then busted a tap from entering a hole off center.

    - Rapid speed is at the maximum recommended speed of 1mhz, actually 1,020,000 to reach 500 IPM rapid. My Z axis actually uses a finer screw and is set at 1,250,000 and never ever causes a problem. Also worth noting, in 2018 when I had this problem it was acting up while jogging the machine as well with speeds much slower then max rapid speed. But it did seem to get worse the faster you go, problem went away at very slow speeds on mpg.

    I agree, it seems like the best thing to do is replace the cable and connector. Ill order some supplies and change it out. Should I use the same encoder input or should I try another to eliminate the input as a possible problem?

    Im open to anything to try and catch it. But its hard to know when this will cause problems again? Could be months down the road, or years?



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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    I have eliminated the encoder as a possibility. The original encoder I was using ran fine for a year or so, when it acted up the first time (in 2018) I changed to a spare encoder and still had the problem when jogging the machine. I left the spair encoder on the machine and later that day the problem disappeared and its been running fine ever since, until just recently. So im pretty sure both encoders are working fine.
    I expect you are correct, but I don't think it 100% proves the encoders are not the problem. Maybe 2 marginal encoders? I have had issues with encoders being not aligned properly and being intermittent. Like when the disk is not concentric with the shaft.

    Like I said before if the position shifts then definitely something related to the encoder or reading the encoder didn't work correctly.

    How about the 5V powering the encoder? Where is it sourced from? What is the voltage?


    Should I use the same encoder input or should I try another to eliminate the input as a possible problem?
    It would be very unlikely for a differential receiver input to function intermittently. But I suppose it wouldn't hurt to use a different channel. If anything I would suspect the screw terminal connector. You might check if the screws are tight. Possibly some corrosion or contamination? BTW there is 470ohm termination on the differential signals. So with power off you should measure about 470 ohms between the + and - inputs. If the connector wasn't making good contact then it would measure higher resistance. I recall you said unplugging the terminal and re-plugging it seemed to change the behavior once.

    Obviously if the problem ever comes back you should not change or touch anything and try to find the cause.

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Quote Originally Posted by TomKerekes View Post
    How about the 5V powering the encoder? Where is it sourced from? What is the voltage?
    The machine has its own DC power supply, very similar setup to standard pc power supply (pc supplys can even be used as replacements) and Im pretty sure I used the 5v supply from this to power encoders. I will double check voltage. I used the same source to power all three so not likely to be the problem.

    It would be very unlikely for a differential receiver input to function intermittently. But I suppose it wouldn't hurt to use a different channel. If anything I would suspect the screw terminal connector. You might check if the screws are tight. Possibly some corrosion or contamination? BTW there is 470ohm termination on the differential signals. So with power off you should measure about 470 ohms between the + and - inputs. If the connector wasn't making good contact then it would measure higher resistance. I recall you said unplugging the terminal and re-plugging it seemed to change the behavior once.

    Obviously if the problem ever comes back you should not change or touch anything and try to find the cause.
    I just had another thought Tom, wondering what you think... Could I jumper the wires from my Y axis encoder input over to an unused encoder input, and if the problem ever comes back I could compare position of both axes in kmotion to see if they are the same? If theres any difference, this should mean I have some kind of poor connection in the screw terminals, or some kind of issue with the differential receiver? I could probably even get my init file to compare positions and warn if they drift off? Any thoughts? Would this be worth doing?



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    Default Re: Problem with Y axis, need help!!

    Hi Mark,

    Could I jumper the wires from my Y axis encoder input over to an unused encoder input, and if the problem ever comes back I could compare position of both axes in kmotion to see if they are the same? If theres any difference, this should mean I have some kind of poor connection in the screw terminals, or some kind of issue with the differential receiver? I could probably even get my init file to compare positions and warn if they drift off? Any thoughts? Would this be worth doing?
    Yes. Use a dummy axis configured to read the encoder. Then compare them in a forever loop in your init file. Note you should grab both encoder readings in the same time slice so you might read them immediately after a WaitNextTimeSlice()

    Regards
    TK http://dynomotion.com


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    Default Re: Problem with Y axis, need help!!

    Are servos DC brushed on brush less? What kind of servo drive? I had an issue years ago with an old Leblond Dynapath lathe with brushed servos, that maybe had similar issue as yours. Was always returning the drive, but problem would creep back after a few months. So i replaced the brushes , re-tuned the analog drives and problem went away.

    Troy

    www.tsjobshop.com, www.homecncstuff.elementfx.com


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    Default Re: Problem with Y axis, need help!!

    Thanks Tom, Ill try and figure out some code to check for this. Feeling much more confident about this now. This should catch any possible issue in the receiver, or screw terminal connections. So if problem comes back again, and both counts are the same, this pretty much confirms the problem is in my wiring or the encoder which is a fairly easy fix anyway.

    Troy, Im using the stock Fadal DC motors and drives. This setup is a little different, the drives dont see the encoders at all, and dont do any tuning either. My encoder signals go directly to Kanalog and Kflop handles all the tuning. The tachometers are gone too, all the the drives do in my case is just amplify the signals from Kflop.



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    Default Re: Problem with Y axis, need help!!

    Hi Tom,

    I have some progress with this issue today! I decided to go ahead and parallel my encoder inputs for Y axis (CH1) over to CH6 to do a double check. And right after doing this the problem popped up again, and sure enough I can see the two channels drifting apart. I set up an indicator and CH1 is moving off (and axis sounds rough at high speed) and CH6 is reading good. So I guess this means the problem is either between the screw terminal block and the pins, or in the receiver itself. And looks like my wiring/encoder should be fine.

    Considering that the problem popped up again right after me doing this, Its likely that something I did here caused it to come back. I have 2 possible theories. First is loose connection between pins and me fiddling with it made it loose again. But how would this allow it to work fine at low speed and not work at high speed? Second theory is that my receiver has some kind of issue and is barely able to read signals at high speed. Now with the encoder signals being send to 2 inputs they are slightly lower strength and this is just enough to cause it not to work? Any thoughts on which problem is more likely? Or something else I haven't thought of?

    Also whats the proper C code to get the current encoder position? I want to do something like this:

    YAxisDifference = Channel1position - Channel6postion;



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    Default Re: Problem with Y axis, need help!!

    A little update. I tried re seating the connector and no change, no sign of corrosion or anything either. I checked voltage on everything and Im getting 5.1v supply to encoders, 3.52V across X axis encoder inputs, 3.31v on Y, 3.63 on Z and 2.83v on my spindle encoder. Interesting that Y is lower then the others, but it should still be well within the range.

    Problem is still there with CH1 input after removing and installing screw terminal so I think I just need to forget about CH1 and move to CH6. Can you help me make the changes to my init file to use channel 6 instead of 1? Why is there 2 input channels for each axis? Is this normal? A little confused here.

    My X axis uses 0 for both, but Y is using ch1->InputChan0=1; and ch1->InputChan1=2;


    ch1->InputMode=ENCODER_MODE;
    ch1->OutputMode=DAC_SERVO_MODE;
    ch1->Vel=1020000;
    ch1->Accel=3500000;
    ch1->Jerk=200000000;
    ch1->P=2;
    ch1->I=0.025;
    ch1->D=0;
    ch1->FFAccel=0;
    ch1->FFVel=0;
    ch1->MaxI=500;
    ch1->MaxErr=300;
    ch1->MaxOutput=1000;
    ch1->DeadBandGain=0;
    ch1->DeadBandRange=2;
    ch1->InputChan0=1;
    ch1->InputChan1=2;
    ch1->OutputChan0=1;
    ch1->OutputChan1=3;
    ch1->MasterAxis=-1;
    ch1->LimitSwitchOptions=0x10;
    ch1->SoftLimitPos=1188720; // set limit to +9.75 inches
    ch1->SoftLimitNeg=-1188720; // set limit to -9.75 inches
    ch1->InputGain0=-1;
    ch1->InputGain1=1;
    ch1->InputOffset0=0;
    ch1->InputOffset1=0;
    ch1->OutputGain=-1;
    ch1->OutputOffset=0;
    ch1->SlaveGain=1;
    ch1->BacklashMode=BACKLASH_LINEAR;
    ch1->BacklashAmount=48; // 48 for 0.0004" 12.192 COUNTS PER TENTH
    ch1->BacklashRate=2000;
    ch1->invDistPerCycle=1;
    ch1->Lead=0;
    ch1->MaxFollowingError=150; // reduced from 300 to hopefully trip if loosing counts
    ch1->StepperAmplitude=250;

    //Pole zero 45, 180
    ch1->iir[0].B0=14.849600;
    ch1->iir[0].B1=-28.946699;
    ch1->iir[0].B2=14.106600;
    ch1->iir[0].A1=1.804700;
    ch1->iir[0].A2=-0.814233;

    ch1->iir[1].B0=1.000000;
    ch1->iir[1].B1=0.000000;
    ch1->iir[1].B2=0.000000;
    ch1->iir[1].A1=0.000000;
    ch1->iir[1].A2=0.000000;

    //Low pass 500
    ch1->iir[2].B0=0.123861;
    ch1->iir[2].B1=0.123861;
    ch1->iir[2].B2=0.000000;
    ch1->iir[2].A1=0.752278;
    ch1->iir[2].A2=0.000000;



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Problem with Y axis, need help!!

Problem with Y axis, need help!!

Problem with Y axis, need help!!