Electrical Noise Causing Axis Jumps

Hi Guys, thought'd i'd post my issue here so some of you gurus could possibly give me ideas to solve my new problem.

Machine is a Mazak VQC 20/40B retrofitted with a 7i92, 7i77 & 7i84. Machine has been working and ran its first parts perfectly fine a couple of days ago. Went to do a test on the weekend and the machine started jumping on each axis and had a complete runaway moment on the z axis. Performing some breif debugging shows this issue only occurs when the spindle is running and the issue disappears with spindle off.

The only difference from the first parts I ran to now was the position of the head in the z axis. Head was close to top of travel for successful parts and low in the z travel when this issue occured. I have attached photos of halscope showing what the x axis encoder velocity looks like without the spindle running and a capture of the x axis jumping (spike in encoder velocity, jogging at 319mm/min) with the spindle running. I get the same issue on all axes repeatably with the spindle running. Spindle off everything perfect. Another issue I now have is even when I run the spindle and do not jog the machine, I get random estops in gmoccapy for no reason (see attached picture) which has to be noise causing this.

I would also like to point out, to see if it is a possible contributor is, I have shielded twisted pairs (earthed at contol side) coming from the encoders on each axis to my custom breakout boards, which then go to the 7i77 through CAT5 cable (see attached pictures). Is it possible noise is being introduced into the encoder feedback through this unshielded cable despite being a short run?

Any ideas to test for what is causing this would be appreciated!

Are you sure noise isn't affecting the command voltage (I assume +-10V)? encoders should be relatively robust, i think it would be strange to count multiple ticks into wrong direction and back again. To me it looks more like axis jumps (because of noise on command) and PID tries to correct.

Thanks for the responses guys.

Andy, the spindle dive is mounted inside the main cabinet with the rest of the drives. Thanks for the link, i'll be sure to scope them out and I must say they are very reasonably priced. As the machine never had a filter on the spindle drive, I would like to solve the problem without adding additonal hardware but if all else fails, thats what i'll be putting in.

Tommy, I resued the original resolver wires as my encoders are only AB quadrature. My machine manual calls out shielded twisted pairs for the resolver cables hence why I reused them but admittedly I havent actually split apart one or the MR connectors to check the cables actually ar shielded and grounded. The shiled/case gound pin is certainly grouded as I check this with a multimeter.

RMU, I feel like you are more on the money here. The axis jumps at a repeatable frequency (consistent timing between jumps) while jogging with spindle on and yes would be strange for the encoder to jump multiple pulses in one direction.

As I get random estops when the spindle runs I suspect I am getting noise on the 10v signal lines as well as my inputs. Would the following scenarios be possible:
- Issue with the 24v power supply generating noise as a result of noise on the AC line due to spindle drive?
-  My 0-10v analog signals wires are just single core cables I twisted as pairs (see wires labeled ER(R)1, ER(R)2, etc in first post), despite the short run, could noise be introduced on them and am I better off swapping to shielded twisted cable? This wouldnt explain random estops as those would have to be from noise on inputs.
- Failing/deteriorated transistors in the spindle drive causing the noise? This wasnt an issue before but now suddenly is so wondering if the drive is failing somwhere.
 
 

jlennox wrote:

As I get random estops when the spindle runs I suspect I am getting noise on the 10v signal lines as well as my inputs. Would the following scenarios be possible:
- Issue with the 24v power supply generating noise as a result of noise on the AC line due to spindle drive?
-  My 0-10v analog signals wires are just single core cables I twisted as pairs (see wires labeled ER(R)1, ER(R)2, etc in first post), despite the short run, could noise be introduced on them and am I better off swapping to shielded twisted cable? This wouldnt explain random estops as those would have to be from noise on inputs.
 

Why and how do you get random E-STOPs? I supposed the machine stopped because it thought an axis "jumped" outside of machine limits, but that seems not to be the case. If you have electrical issues with ESTOP triggering via noise, fix that first. E-STOP usually is a loop of "N"ormally "C"losed switches that open when actuated. This way broken or faulty ESTOP chain won't let you activate the machine. Hard to imagine you can influence that with induced noise?
Check for loose connections and if everything is grounded properly. Differential signals also need ground (usually).
If you can use an oscilloscope, check signals with spindle on/off, but be careful to connect probe gnd very near where you pick up the signal.