servo jitter

[LccJester]

We have noticed servo jitters on all of our machines lately. Not sure how long this has been going on but all of our machines are doing this and it has cost us several servo drives. I suspect incoming power problems but haven't been able to find the proverbial smoking gun. Has anyone else ran into this and what should I be checking?

 

[DDoug]

We have noticed servo jitters on all of our machines lately. Not sure how long this has been going on but all of our machines are doing this and it has cost us several servo drives. I suspect incoming power problems but haven't been able to find the proverbial smoking gun. Has anyone else ran into this and what should I be checking?

"Machines" ??? what kind/flavor ?

 

[Milland]

Talk to your electricity provider. Sometimes they have power monitoring equipment that can be patched into the incoming lines to take a record of spikes or other variables that can cause issues.

The other thing you can look at is filters for incoming power. There's some that will take high current or voltage spikes and dissipate them before they get to the machines. Not cheap, but better than repairs and downtime.

 

[LccJester]

Okuma Mazak Dainichi and Ikigai cnc lathes and mills

 

[Vancbiker]

What was the drive failure? In modern drives, the AC is turned into DC then back to AC, incoming power issues are very unlikely to cause jitter.

What is the amplitude of the jitter? Enough to see axis movement?

Really going to need more info to help figure out the

 

[LccJester]

Haven't seen any actual movement just load spikes while idle on as well as servo osculating sounds. They are all older machines ranging from 1985 to 1998. I've had servo lag alarms, velocity unit power too low, soft phase alarm. all on different machines.

 

[Vancbiker]

Those alarms should not have caused a drive failure. Low voltage and phase loss alarms however do point to power issues.

Describe the spikes. Servo oscillation with no notable axis movement often points to looseness or wear in some portion of the drive mechanism. The resulting loss of damping of the servo allows the servo to oscillate.

 

[Strostkovy]

Are they AC or DC servos? If it's an old transformer rectifier power supply feeding them then you should check the capacitors.

 

[DDoug]

Yes, the power co have portable line recording machines, that they can bring out and leave connected to your incoming power for a week or so.

Maybe poking around with a FLIR camera at your main panel would show a hot spot, and loose connection or 2.

 

[MaxPrairie]

We have noticed servo jitters on all of our machines lately. Not sure how long this has been going on but all of our machines are doing this and it has cost us several servo drives. I suspect incoming power problems but haven't been able to find the proverbial smoking gun. Has anyone else ran into this and what should I be checking?

I would start from square 1. If you here your drives making a funny noise, check the incoming line voltage and see if it has any variation. If it doesn't then start checking things downstream. You aren't running a phase converter are you?

Addition: Sounds to me like you are losing power to one leg. I would get the power company out there and do some checking. At least you would have some documentation that you are having issues if you needed to go back on them for your issues.

 

[LccJester]

We have found that one of the legs was dropping voltage. With all three legs equalized the servo flutter is gone. Now we have to figure out what is dropping power on that leg.

 

[Strostkovy]

We have found that one of the legs was dropping voltage. With all three legs equalized the servo flutter is gone. Now we have to figure out what is dropping power on that leg.

Have the power company tell you who all is fed by your transformer. We have an RV sales lot next door that had too many trailers ACs one one phase that was adding a 2V drop to our already lowest leg.

 

[CITIZEN F16]

Have the power company tell you who all is fed by your transformer. We have an RV sales lot next door that had too many trailers ACs one one phase that was adding a 2V drop to our already lowest leg.

I am lucky my property is very close to a substation, I am second to last on our line and probably the heaviest user on that line. I have the same issue, I call it a stutter on both x and z on a fixed headstock lathe. It will only do it when the shop is cold and the machine hasn't warmed up. A shop temp of 75f+ or blowing heat into the cabinet before power up and it doesn't happen. I even sent the dual axis drive to a place I trust and they could not recreate the problem on a simulator. Fanuc OT control.

 

[MaxPrairie]

We have found that one of the legs was dropping voltage. With all three legs equalized the servo flutter is gone. Now we have to figure out what is dropping power on that leg.

Has a new business gone up lately? Or are they not pushing enough coal into the boiler? Always have fun blaming my dad when the power goes out.

 

[npinson]

At a previous shop location, I had a similar problem. It turned out one of the tap connections from a large pole mounted transformer had corroded on one phase. The connection must have been pretty bad for a while, and once the shop was pulling some amps a phase would go really low. It was worse on windy days. It dropped a single phase from 240V down to about 160V. Ended up calling power company and they had to repair the connection to the transformer. They gave me the union splice that was bad. Was nearly melted away because of heat generated from the poor connection.


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