JMC servo "jerk"

[Kars-cnc]

By the way, is the jerk problem similar for both directions of the axis?

[mkuivamaki]

Actually now when you said it, I'm not sure. I'll try to test can I get them at both directions.
Also was thinking could the JMC signal connectors be so unreliable that there could be random miscontacts during vibration etc.?

[Kjelt]

I personally hate the JMC connectors, cheap and not comfortable.
The best way for the control signals is to use a not too thick multistranded cable, strip and insert it and pull softly to make sure good contact is made. Using cable ferrules that I usually do with multistranded wire is not recommended with these clamps since a soft pull is enough to let them get loose again (in some cases). So check your cables.

For the high low or low high that does not matter but make sure the duty cycle is 50% and that the pulse frequency is 10% lower than the max allowed for JMC.

[mkuivamaki]

I have currently tinned RJ45 wires. I know, not so good way to do it. Currently I have ordered Ölflex servo cables (2x4x0.25 + 2 x 1.0) and will do new wirings for the motors, this time not using ferrules or tinned wires. I know some people will use also hot glue to secure these JMC wires in place, those connectors are poor indeed.

[Kjelt]

Again softly pull on the wire to see if they are clamped correctly.
If clamped correctly then measure the connector with ohms on mulimeter to the other side to see if really connected.
UTP ethernet cable can be ok, I know more people that use it. But if the pull test fails, restrip and insert witout tinning, that could work better.
And ofcourse as always mechanically decouple the entire cable so no mechanical forces can be exerted on the connector during movement.

[WillyH]

The JMC connections are indeed something to watch out for. I had initially used ferules with a thicker, colored and insulated end, but this prevented the cables from being inserted next to each other. So, I had to use ferules without insulation/colored ends. It is almost impossible to install a small stranded cable without using a small screwdriver to install the cables sufficiently deeply and securely. You can push on the ferules with the small screwdriver. Had no problems with the (400W) JMC servos.

[Kjelt]

You can push on the ferules with the small screwdriver. Had no problems with the (400W) JMC servos.

That is not advised because you will go beyond the optimal clamping force of the clamp, you will strevh the clamp.
If pushing the connector button and softly pulling the wire will not release it you know the diameter of the wire+ferrule is too thick.
These kind of clamps are suited for direct clamping of stranded wire just as for instance the common household wago 221 and 222 series.
Too bad they use some inferior brand clamps, if they were Phoenix Contact or Wago you would not have any issues.

[mkuivamaki]

Would it be possible to replace those connectors by some good brand products? What is the connector type exactly?

[Kars-cnc]

Replacing the connectors is only useful after it has been proven that they are causing your problem. I immediately believe all those who say the connectors are of poor quality, but I didn't experience any problem with them and many others here also have used them without problems.

If your cable relief at the servo is solid and close to the connector, chances that jerk during such slow and steady movement is caused by the connector are very small (assuming the movement does not cause any strain to the cables).

You have one axis that is not showing this problem. My recommendation is to use that to find the root cause. Swap things between this axis and a faulty one. I know it is scary to intervene in something that is working properly, but it is your best chance to discover the real problem. Remember, the proper working axis is useless as long as the others aren't.

[mkuivamaki]

Yes that is how you should do the troubleshooting. I wouln't be here asking if I had found out already some differences. I have already done what you suggested: swapped motors, PSU's, cabling etc. The only differences between X and Ys&Z are:

- X does have timing pulley, other motors are connected to ballscrews by "spider" coupling
- cable routing is a bit different with every motor (Z has the most comlicated/longest route, Y-motors has the easiest/shortest route)
- X is not crosscompensated in EdingCNC (but tested without crosscompensation so it is not a solution)
- dual Y-motors does have their own common PSU, X & Z does have their own. Tried to swap them and also tried to drive one motor / one psu

[WillyH]

You can push on the ferules with the small screwdriver. Had no problems with the (400W) JMC servos.

That is not advised because you will go beyond the optimal clamping force of the clamp, you will strevh the clamp.
If pushing the connector button and softly pulling the wire will not release it you know the diameter of the wire+ferrule is too thick.
These kind of clamps are suited for direct clamping of stranded wire just as for instance the common household wago 221 and 222 series.
Too bad they use some inferior brand clamps, if they were Phoenix Contact or Wago you would not have any issues.

It's not like I had to apply any significant pressure with the screwdriver. The ferules were clamped to an Igus 0.5mm² flexible cable. I could not push the cables (with ferules) completely into the JMC connection because the cable was too flexible and without a ferule the connection was not reliable at all as I first experienced, when installing the second or third cable the first connection already came loose again. I felt like the ferules were a bit too short and needed an extra push for the last 2 or so mm.

[mkuivamaki]

Yesterday I received two used 480W SDR (Mean Well) power supplies and made some quick tests. Again Z&X have their own psu and dual Y motors have their own.
I immediately noticed that this PSU is far more better choice for JMCs than PSP. I already raised acceleration 50% easily with lower psu wattage! No system errors during stresstests. During one hour tests no single "shocks" either.
So could it be that PSP type psu is not good alliance with JMC? Anyone knows what is exactly technical difference between those two psu?

[serum]

Like i said back in march, I have heard another story with those specific 600W psp that was acting up on acceleration/de-acceleration with a servo connected meant for CNC.

It all depends on the control-loop and the speed the SMPS is capable of adjusting/correcting the required signal. I have no idea what the specific technical difference between these PSU's are, but it seems that the psp600 is not realy suited for a dynamic load with lots of peaks and bumps. Or perhaps it's a combination of the JMC's and the SPS. I know that SMPS can become unreliable if they are not used for their intended purpose. Perhaps you can try to get in touch with meanwell and ask if they can advice a matching power supply or perhaps they can shine their light on the situation/issue.