ON topic- More Y-axis OverVoltage- Random consistentcy frustration

Still fighting a Persistant Y-axis OverVoltage error. The machine will run fine for hours at a time, then suddenly alarm the Y-axis and shuts
down.
But here is a consistent symptom. Yet completely random. It ONLY happens during the first programmed Z-axis rapid/plunge move when the spindle is running HIGH RPM. Never at low RPM. And never consitently. Only 1 out of 20 times or so....Vibration? Current drop?
Mori first suggests the Y-axis motor harness is chafing somewhere. So far no evidence of this. More inspection required. Second suggestion, (by everyone) Bad brushes/armature. Inspected & cleaned (D.C. Servos) Next step, get the motors armature re-surfaced., if only we could finish the current job, first.
Will swap x & y cables to see if the problem moves, next. (cable or motor?)
Any more ideas?
ca
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While the motors are out, be sure to have them baked. I forgot that part before. Also, you might have coolant contamination of the cables/connectors themselves.
The fact that you need a Z plunge indicates that the Z drive is in regen mode (Suddenly! acting as a generator) The Z driv eis holding up the head, and then Suddenly! letting it go, and getting power back from the motor.
The load dump (braking) resistor is suposed to burn that suge of power and prevent the DC bus from going high. (Overvoltage)
I don't know how to inspect the braking resistor circuit. You could start and stop the spindle repeatedly, and check to see if the braking resistor is getting hot, (Don't touch it unless you like to get fried, yourself).
Somebody else should have a better idea how to test the braking resistor. Doesn't the Haas or Fadal use a heating element from a stove? Along with the resistor itself, there is the circuit inside the power supply that dumps the bus to the resistor. Some machines also have a circuit breaker in the braking circuit.
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Half-nutz wrote:

So you think the Z-axis brake circuit is failing. Why is the Y-axis ALWAYS the OverVoltage? Never the X-axis. Once the Z axis alarmed OverCurrent and the Y-axis OverVoltage, while the machine was idling unattended. but since it is always the Y-axis that alarms now, while running.
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Not the axis brake! The braking resistor. Very different.
The spindle and servo's may all be driven from a power supply. Those power supplies usally have a "braking resistor circuit" on them. What is does is monitor the DC power supply, and if it starts to overvoltage, it hooks a big resistor onto the DC bus, to absorb the overvoltage.
When a servo is moving, it is moving a mass, like the table in a rapid move. When it tries to stop that motion, the servo motor acts like a generator, and puts power back into the power supply. It is under these "braking" conditions that the circuit kicks in, and dumps the excess power into the "braking resistor" On the HAAS or (?) Fadals they actually use a heating element out of a stove.
This is nothing to do with the brake on the axis. That is only used for power off, to hold the axis from moving.
There should be a large resistor someplace on the machine, maybe hidden in the power supply, or in a seperate box.
Since it is kicked in when an axis is trying to stop, it is interesting the relation to the Z axis peck. Once that Z axis is moving down, it will want to dump a gob of power into the power supply trying to stop that Z axis as it is moving down. This is electrically, a braking operation. (But not using the Z axis brake.)
Something to look into anyway.
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Half-nutz wrote:

Each axis/servo drive on this machine has its own braking resistor. They are mounted behind the drives. I believe there is a triac that does the regen switching.
Interesting, today I was able to experience the error, when I let the z-axis rapid all the way to the r-plane. The time before I stopped the move about 1 inch short. No alarm. hmmm....
ca
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wrote:

Assuming there's a tach then suggest measure it's output from the z servo motor at full rabbit and get back to us--multimeter setting will be dc, and a typical reading is 7 volts per 1000 rpms--write up a proggy that causes the z to go all the way in minus then all the way in plus then repeats--(reverse your meter leads if the needle always pegs left)
Fwiw, I have a funuc 3t as well as a 6m that is been doing exactly the same shit lately ( CNC goes estop due to OV led alarm at servo amp )--no big deal and no time to zero in at the moment as to the exact cause and so for the time bean we simply reduce the max rapid traverse parmeter for the offending axis.
--


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So you think the Tach output is bad? Dirty Tach, etc...
ca
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servo
and
causes
same
deal
the
offending
Yes seems like if your tach output is too low then your ref voltage will try and compensate for what appears to be inadequate motor velocity, essentially causing the motor to overspeed.....not a problem till it comes time to decellerate down to a stop....at which point generated back-emf will exceed the dc buss regulator dissapation capacity
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the
dc,
big
try
essentially
exceed
Also, external regen unit are available and one could be attached to the dc buss if you determine the system isnt working in your drive :
http://www.a-m-c.com/content/prods/descriptions/shunt_regulators.html
--






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clay wrote:

Your load resistor is probably open or if you have a balancing cylinder on the Y it may not have the proper pressure set. This holds if the machine is a HMC. If you have a VMC the balance cylinder would be on the Z axis.
John
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john wrote:

Another possible cause would be leakage in two motors to ground. This will cause all types of wierd problems. Meg both motors to ground. dont forget to disconnect the servo drive units before you put the megger on the motor.
John
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john wrote:

VMC. If the load resistor was open would it not happen everytime? There is no balance cylinder, this machine uses a counterweight only. Again, why would it start failing now? It only happens 1 of 20 times, or more. Balance resistor with a bad connection, High RPM vibration? hmm....
ca
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clay wrote:

It happens when you exceed the setting of the voltage sense circuit. Tool weight, deceleration rate are all factors when the drive goes into regeneration mode. it could even be that the pulleys on the counter weight are not running smooth. Another thing you could try is to slow down the rapid speeds and see what happens. Just program a high feed rate rather than a full rapid move. it could even be the drive reference adjust is set too high for the machine.
John
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