dondon_alba
Member
OP
Both motor windings are having an infinite reading and healthy.
Crane Jerk Problem during starting and stopping
- Thread starter dondon_alba
- Start date
Both motor windings are having an infinite reading and healthy.
kamenges
Member
Did you perform at least a static autotune on the motor pair? I would recommend a rotating autotune but that may be a little difficult for you to do mechanically.
How do your drive torques look at boht low and high speed? If this is a mechanical issue you wouldn't expect the load to decrease any as speed increases.
Keith
How do your drive torques look at boht low and high speed? If this is a mechanical issue you wouldn't expect the load to decrease any as speed increases.
Keith
leitmotif
Member
Well if the VFD setup has been operating trouble free for seven years I think fairly safe to assume that VFD / electrical is not the issue.
That goes over to mechanical.
You mentioned problems with electo mechanical brake. FOR SURE I would get them fixed before I spent one minute looking at anything else.
FOR TEST PURPOSE ONLY
Disconnect the brake electrically and have mechanic back off the adjustment for the brake to ensure NO drag - test it in this configuration and see if improvement. Leave lots of room for coasting - you have NO brakes.
Dan Bentler
Gil47
Member
Have you measured the current to each drive motor individually and are the fairly well balanced in there load as I would expect them to be.
My thoughts are that each motor could be running but only one is driving the forward backward motion ( say because of a stripped gear key way ) this could cause it to have a lurching action in its direction movement but would still look as if everything was still intact.
My thoughts are that each motor could be running but only one is driving the forward backward motion ( say because of a stripped gear key way ) this could cause it to have a lurching action in its direction movement but would still look as if everything was still intact.
I agree with Dan's on his point here.
How is the brake hooked up. Is it hooked to the drive, were the drive is controlling it or is it controlled by the crane PLC?
Here is one way test what Dan is talking about safely. Have a switch or another contactor to release the brakes, this way you have better control over the testing.
How is the brake hooked up. Is it hooked to the drive, were the drive is controlling it or is it controlled by the crane PLC?
Don - did you ever resolve this issue?
I have been struggling with almost the exact same issue in the same application - a multi-purpose bridge crane used for a carbon anode baking furnace.
PowerFlex700VC 125A drive drawing from a common DC bus supplying the bridge, trolley, and anode hoist drives. The bridge drive runs two 20hp Reliance RL-model bridge motors controlled by a ControlLogix PLC via ControlNet, all engineered by Rockwell and installed new. No encoder on either motor. The drive nor the individual motor overloads never trip. Been a problem every since the installation in 2007. Rockwell field engineers have been in four times to no avail.
The local Rockwell distributor has said he'd like us to go ahead and try another manufacturer's drive to see if that solves the problem. Say what???
Currently running in V/Hz mode, with the speed regulator just on the verge of being turned off - seems to be the best solution, but nowhere near acceptable. If I'm not ready when the operator takes off, the repetitive jerking occuring on about a 1/2-second frequency interval just about knocks me off my feet. The operators refer to this crane as the bucking bronco.
An identical sister crane has the A-B 1395 DC drives and another larger crane of similar function has the Reliance GV3000 AC drives - both ride like Cadillacs. The problem-child crane used to run well with its 1395 drives, until the conversion. Of course, the drives that have been proven to work well are now obsoleted.
The jerking seems to be the worst when taking off from a stop, trying to position at slow speeds. Wide-open throttle take-offs aren't too bad but not great either. Joystick verified for clean signal. Motor brakes verified for full release. Several parameters such as jerk rate, accel/decel rates, current limits, speed regulator gains and the like have been run from one extreme to the other to find a happy/happier medium. Once things are moving at, say, greater than 10-15Hz, it runs smooth. Decel is pretty good until just before zero speed.
The amperage trace on accel shows the fluxing current spike on start-up/energization, then what appears to be a upright half-wave rectified pattern starting out ranging from 0.5 minimum to 1.0 maximum of the drive FLA limit, then tapering off to a relatively steady current draw in 3-5 seconds.
Would appreciate any suggestions, as my magic hat is out of rabbits.
I have been struggling with almost the exact same issue in the same application - a multi-purpose bridge crane used for a carbon anode baking furnace.
PowerFlex700VC 125A drive drawing from a common DC bus supplying the bridge, trolley, and anode hoist drives. The bridge drive runs two 20hp Reliance RL-model bridge motors controlled by a ControlLogix PLC via ControlNet, all engineered by Rockwell and installed new. No encoder on either motor. The drive nor the individual motor overloads never trip. Been a problem every since the installation in 2007. Rockwell field engineers have been in four times to no avail.
The local Rockwell distributor has said he'd like us to go ahead and try another manufacturer's drive to see if that solves the problem. Say what???
Currently running in V/Hz mode, with the speed regulator just on the verge of being turned off - seems to be the best solution, but nowhere near acceptable. If I'm not ready when the operator takes off, the repetitive jerking occuring on about a 1/2-second frequency interval just about knocks me off my feet. The operators refer to this crane as the bucking bronco.
An identical sister crane has the A-B 1395 DC drives and another larger crane of similar function has the Reliance GV3000 AC drives - both ride like Cadillacs. The problem-child crane used to run well with its 1395 drives, until the conversion. Of course, the drives that have been proven to work well are now obsoleted.
The jerking seems to be the worst when taking off from a stop, trying to position at slow speeds. Wide-open throttle take-offs aren't too bad but not great either. Joystick verified for clean signal. Motor brakes verified for full release. Several parameters such as jerk rate, accel/decel rates, current limits, speed regulator gains and the like have been run from one extreme to the other to find a happy/happier medium. Once things are moving at, say, greater than 10-15Hz, it runs smooth. Decel is pretty good until just before zero speed.
The amperage trace on accel shows the fluxing current spike on start-up/energization, then what appears to be a upright half-wave rectified pattern starting out ranging from 0.5 minimum to 1.0 maximum of the drive FLA limit, then tapering off to a relatively steady current draw in 3-5 seconds.
Would appreciate any suggestions, as my magic hat is out of rabbits.
Peter Nachtwey
Member
Have you tried accelerating slower?
Do you only have this problem when there is a swinging load underneath?
Do you only have this problem when there is a swinging load underneath?
Tried accelerating slower - yes. The as-found parameter was 3.5 seconds, same as for the other two cranes. Have run it up to 8 seconds without noticing any significant difference.
The problem exists at all times - although some operators have learned better than others how to manage the jerking to a lesser level - I haven't yet picked up on what they do different.
The only real additional load is connected by a rigid beam and is relatively small (~8,000 lbs) as compared to the estimated total weight of the crane (~80,000-100,000 lbs?).
The crane structure has been inspected for flexing, thinking we may be hitting some kind of natural frequency - but nothing was found here either.
To better explain the crane's functions - it inserts sets of three anodes measuring about 57 inches long by 30 inches wide by 26 inches deep and weighing about 2600 pounds each down into flue sections/compartments for baking and then their removal afterward. Imagine the old board game 'Operation' and you have a pretty good idea of this setting and picking process requiring good stable positioning. It also covers the anodes with coke fines for the baking process and sucks up the coke fines afterwards prior to anode removal - which includes various retractable ductworks, hoppers, dust collectors, high-volume blowers and low-volume air compressors for the coke application and removal. Auxiliary wire rope hoists are on the crane for the moving of the burners around the furnace. Thus, the aptly named multi-purpose (MP) crane
Other notes - amps seem to be balanced both between phases and between motors at steady state, phase impedences are balanced, and meggar readings are good. The problem hasn't seemed to change in nature over the year-and-a-half I've been involved, so ruling out a failing component.
My next thought is to run the joystick voltage reference straight into the drive instead of being conditioned through the PLC and passed over ControlNet at the 50ms update rate - but I admit, this is grasping.
The problem exists at all times - although some operators have learned better than others how to manage the jerking to a lesser level - I haven't yet picked up on what they do different.
The only real additional load is connected by a rigid beam and is relatively small (~8,000 lbs) as compared to the estimated total weight of the crane (~80,000-100,000 lbs?).
The crane structure has been inspected for flexing, thinking we may be hitting some kind of natural frequency - but nothing was found here either.
To better explain the crane's functions - it inserts sets of three anodes measuring about 57 inches long by 30 inches wide by 26 inches deep and weighing about 2600 pounds each down into flue sections/compartments for baking and then their removal afterward. Imagine the old board game 'Operation' and you have a pretty good idea of this setting and picking process requiring good stable positioning. It also covers the anodes with coke fines for the baking process and sucks up the coke fines afterwards prior to anode removal - which includes various retractable ductworks, hoppers, dust collectors, high-volume blowers and low-volume air compressors for the coke application and removal. Auxiliary wire rope hoists are on the crane for the moving of the burners around the furnace. Thus, the aptly named multi-purpose (MP) crane
Other notes - amps seem to be balanced both between phases and between motors at steady state, phase impedences are balanced, and meggar readings are good. The problem hasn't seemed to change in nature over the year-and-a-half I've been involved, so ruling out a failing component.
My next thought is to run the joystick voltage reference straight into the drive instead of being conditioned through the PLC and passed over ControlNet at the 50ms update rate - but I admit, this is grasping.
leitmotif
Member
Just to ensure one VFD driving a 20 HP motor on either end of bridge? Motors are not line shaft connected but run independent?
Saw several cases where bridges on cranes got out of parallel on tracks ie "crabbed". Solution was to chain one end or lock that hydraulic brake and drive other end til square. This was line shaft driven so one would think stay square - but,,,
Check to ensure it is running square and not crabbing.
Measure the torque on each motor shaft and see if one gearbox is demanding more than other - ??? Gonna take a little tooling and a fairly good size torque wrench or multiplier.
Dan Bentler
Saw several cases where bridges on cranes got out of parallel on tracks ie "crabbed". Solution was to chain one end or lock that hydraulic brake and drive other end til square. This was line shaft driven so one would think stay square - but,,,
Check to ensure it is running square and not crabbing.
Measure the torque on each motor shaft and see if one gearbox is demanding more than other - ??? Gonna take a little tooling and a fairly good size torque wrench or multiplier.
Dan Bentler
Yes, a single drive running two 20hp motors, one on each end of the bridge, that are not mechanically connected.
Will have another look at crabbing. One of the early findings was that one of the brakes was not functioning, with the thought that at stop, that end of the bridge may roll out of square with respect to the rails and the jerking was a result of getting lined back up true again.
Hadn't thought of actually measuring the individual motor torque. Will have to do some figuring on how to do this, while staying within the plant safety rules.
Thanks for the ideas!
Will have another look at crabbing. One of the early findings was that one of the brakes was not functioning, with the thought that at stop, that end of the bridge may roll out of square with respect to the rails and the jerking was a result of getting lined back up true again.
Hadn't thought of actually measuring the individual motor torque. Will have to do some figuring on how to do this, while staying within the plant safety rules.
Thanks for the ideas!
leitmotif
Member
Maybe flogging a dead horse BUT
IF the brakes do not set equally then one end rolls more than other.
ASSUMING INDUCTION MOTORS then if one motor shaft torque demand is higher than other
(they will NEVER be exactly equal ALL the time)
then the higher load motor runs with more slip thus slower.
IF the brake problem and higher torque are both on same end then your problem is not 1 + 1 = 2 but maybe synergistic ie
1 + 1 = 3 (or 4?)
Yeah repairing cranes is a tough challenge from the safety end of things. Not much room, coupla guys, concentrating on trying to fix the thing, and having to remember gravity seems to be stronger 50 or 100' up.
Dropped tools from cranes and sailboat winch handles accelerate instantaneous to speed of light when leave your hand.
Dan Bentler
Last edited:
kamenges
Member
Are you running with any slip compensation? If so, you may want to try and turn it off.
Does anyone know why "they" don't use synchronous motors on these things?
Keith
Does anyone know why "they" don't use synchronous motors on these things?
Keith
leitmotif
Member
1. Too expensive ??
2. Synchronous can be hard starting and take special controls to do so ??
Dan Bentler
The mechanical brakes are more of a 'parking' brake, not used to slow the crane but just hold it in place - except on E-Stops. IIRC, the logic is something like when there is a zero speed reference AND the calculated speed has been less than +/-0.5 Hz for 5 seconds, then the brakes set.
Slip comp is off.
Have talked with Rockwell about changing the default current regulator gains - but they very strongly recommended against it, almost panicked that I even brought that up. Also I was concerned about the size of the drive (125A) versus the motors (52A summed FLA) - always have gone by the rule that the drive should be no more than 2x FLA, but the TechConnect rep wasn't too concerned about the degree of mismatch.
One of their field engineers recommended a 1/4 speed switch - where when close positioning and small moves were required, the operator would flip the switch and the max joystick reference would be 1/4 max speed to reduce the speed regulator errors. Had concerns that the operators would forget which speed range they were in - another mode of failure.
Since the bridge drive is supplied from a common DC bus supplying all three crane drives - monitored the bus voltage - eh, stays very stable.
Slip comp is off.
Have talked with Rockwell about changing the default current regulator gains - but they very strongly recommended against it, almost panicked that I even brought that up. Also I was concerned about the size of the drive (125A) versus the motors (52A summed FLA) - always have gone by the rule that the drive should be no more than 2x FLA, but the TechConnect rep wasn't too concerned about the degree of mismatch.
One of their field engineers recommended a 1/4 speed switch - where when close positioning and small moves were required, the operator would flip the switch and the max joystick reference would be 1/4 max speed to reduce the speed regulator errors. Had concerns that the operators would forget which speed range they were in - another mode of failure.
Since the bridge drive is supplied from a common DC bus supplying all three crane drives - monitored the bus voltage - eh, stays very stable.
If your other cranes are the same ad have the same manufacturer.
What is the chance that there may be a loose connection to one of your park brakes.
It is possible that the power is either dipping or dropping off as the load is increased.
Also
Check the supply bus rails to the crane itself - I have had experience with the rails not being installed correctly.
They were not fitted with the metal clips that stop them from coming apart
What is the chance that there may be a loose connection to one of your park brakes.
It is possible that the power is either dipping or dropping off as the load is increased.
Also
Check the supply bus rails to the crane itself - I have had experience with the rails not being installed correctly.
They were not fitted with the metal clips that stop them from coming apart
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