Torq-Cut 22 Z-Axis Over Current Alarm

[md63825]

The previous owner of this Torq-Cut 22 that I recently purchased told me that they were having problems with rapid movements in the Z axis. When the machine rapids in Z, I get a "Z Axis Drive Over Current Fault". What they advised as the work-around was to change all G00 moves to G01 movements at 40 IPM. Did it and it works. I would still like to fix the root cause. Any advise?

[PMW1]

If there is any noise in the axis it could be the bearings. They might be putting excessive load on the axis.

[md63825]

Thanks for the reply. No, spindle is one of the quietest I have ever heard. Machine is in pristine condition. Came out of Georgia Tech lab. I changed my Max and Jog rate to 100 ipm in parameters and machine does fine. Seems like anything over 150-200 ipm and I get the Over Current Fault. Has something to do with the servo drive I think. I am trying to figure out what Z-axis servo drives it is using.

[cncbpt]

Look at the z axis motor and see if it is the parvex motor
The tag can be read on mine from the back side looking down in the column
These machines dont have a counterweight on the z axis and the original motor was not up to the task of driving the z axis up under high loads as in a rapid.
They were than retofitted with the Parvex motor and higher ouput drive to solve the issue
I believe there is a parameter that could be changed to reduce the maxium feedrate during a z axis rapid call

[md63825]

It is a Parvex motor. I changed the parameters for Max and Jog rate to 100 ipm. That seemed to fix the issue for now. I was talking to another machinist recently and he said he reduces the default max feed rates on the Z-axis on all his machines to reduce the wear and tear on the servos. Would still like to know what the root problem is. Thanks for your response.

[md63825]

Guess I spoke too soon. After changing the jog rate to 100 ipm, I no longer get an Axis Drive Over Current Alarm, now I get a "Following Error Limit Exceeded" alarm. It all revolves around the Z-axis. Looked at the Maintenance Page and the Pos-Err for Z was .050. I get that because the axis was jumping as it moved in the + direction. What stands out to me is the column next to it. Under DAC-CMD all the other axis read -1024, but Z reads -967. When in the jog mode, I can jog X and Y and that number fluctuates a little but returns to -1024 once I stop. The Z axis on the other hand, when I move down in the - direction, it looks ok, but when I move up in the + direction, it drops to about -870. And this is when I get either of the alarms is when it is moving up in the + direction. Any help is greatly appreciated.

[machintek]

Remember that there is no counter weight. That is why Bridgeport retrofitted these machines with the much larger Parvex motor. But this is still a DC motor with brushes. It is possible that they are worn down. i have yet to replace a Parvex motor or brushes. It is more likely that the axis drive board has issues.

George

[md63825]

Thanks for your reply. I am working with Gary Geltz (not sure if you know him) and he said the same thing, that he has never replaced one of these Parvex motors. This has taken a strange turn though. At some point while in the possession of Georgia Tech, McDaniel Machinery added Advanced Motion Controls "Brush Type PWM Servo Amplifiers" on each of the axes. Even stranger is they are connected in series with the original axis drives. Original axis drives are still connected to BMDC board. My understanding from a gentleman at GT was it was a bridgeport upgrade. According to Gary definitely not. Thought the installation looked kind of sloppy anyway. So, Gary is checking on that. Why, we don't know yet.

I just ran the machine for two hours roughing an aluminum part down with no problems. Program went to perform a tool change and Bam, Z Axis Drive Over Current Fault. Cleared faults, re-homed the carousel, did a program restart, ran next tool and started noticing jerky movements in Z rapid moves. Wasn't long til she faulted out with the over current alarm again. So, I opened the electrical cabinet and this Brush Type PWM Servo Amplifier on the Z-axis is warmer than the others. But, I did notice that the cooling fan on the left (facing the inside door) is dead. I'll replace it Monday. One on right is still running. Anyway, then I climbed on top of the machine, removed the shroud and felt the Z-Axis servo motor. Very warm, not hot, just very warm. I am going to let her cool off for a while and try to restart the program again.

I haven't had the machine long. Since about end of July. I bought it through a machine reseller that acquired it from Georgia Tech. What kind of stinks is they (Georgia Tech) told this guy about the Z-axis problem when he bought it from them. He never relayed that information to me because he says it never gave him a fault while it was in his possession. I guess I'm stuck with it so I have to get it fixed. Hard on a small owner/operator though.

[machintek]

Say hello to Gary for me. We are both part of the Jurassic service department. I have known him for many years. I still work for McDaniel Machinery (21 years now). And the inside of your machine does not sound "stock." I have never been to Georgia Tech but maybe Scott or Kyle who work with me may have been. None of us would parallel or serially connect axis drive boards. It is beyond their capability to do such a thing. I would be most interested to see such a arraignment. It is more probable that someone who did not belong fooling around with this machine, made the modifications. Did Gary have hands and eyes on the machine? ask him to call me. Maybe it is being described incorrectly.

George

[md63825]

George, I will be talking to him next week so I will mention that you said hey. Gary definitely sounds like he knows his stuff.

I don't want to get anyone in trouble at McDaniel Machinery. I was only told by GT contact that he thinks the techs name was Adam from McDaniel Machinery that installed these components. He had no maintenance records for the machine so he could be mistaken. He said Gary knew Adam so Gary may be trying to contact him to find out for certain. Apparently Gary worked on this machine years ago. He made the comment that it was a well taken care of machine and GT never ran it hard at all.

Gary has not touched this machine first hand but I did send him some pics. I have attached those pics showing the components. I originally sent these photos to the company I bought the machine from to show them that upon initial inspection of the machine after its arrival, these components were laying loose in the cabinet. They were surprised and apologized for overlooking it. There was one wire that was not even connected (holding it in pic). I connected it to the terminal on the relay next to the drive after comparing it to the other relays.

I am swapping the Y and Z Amplifier to see if it changes anything. All of these "Brush Type PWM Servo Amplifiers" are identical so I don't see where it would hurt anything. If the problem doesn't go away, I figure I can deduce that it's not the amplifier. Consequently, if problem moves to "Y" axis then I know it's the component. Contacted Advanced Motion Controls yesterday and that is what they suggested. Have any idea what these are for exactly? Gary seemed stumped.

[md63825]

Think I can rule out the amplifiers that were added as being defective. They may still be contributing in some way. Let the machine cool for a few hours and re-started my program to run the other half and again, about two hours in and over current alarm strikes again.

Can I check the brushes without removing the motor? I still need to measure the resistance on the motor armature. Need to find my meter first.

[machintek]

These drives are being sold by EMI as replacements for the original V2XT and EZTRAK drives. Never seen one used in a TC-22 as a replacement nor as augmentation. And what is the purpose of the relay?
This is why I do not answer questions involving machines that are retrofits or modified. Too many variables. Stock machines keep me busy enough.
I will check with my parts manager to see if he recalls such drives being sold to Georgia Tech and to what end. I will also check with EMI.

George