Ez Path II aka Ol' shakey

[klxrcr]

An ezpath I run at work frequently has a shakey x axis, The "bridgeport" repair guy thinks it needs a new servo motor, which dose not make sense to me.

It used to shake constantly a small ammount (more than dithering) until one day it was left by its self for a while (hours) and shook until it smoked the servo.

A new servo was installed and now it only shakes after rapid moves until it calms down 5-10 seconds then its stable. but this sounds like and under dampened servo drive to me. Right now its overshooting its position by about .030" if the F'ed up threads it produces are any indication.

It can still make good parts, because I'm good, real good.

so what do you guys think?

[machintek]

The original EZPATH 1 had DC servo motors. They had a velocity loop (tach). If there was a broken wire to this, it would oscillate back and forth.
Check your wiring diagram. Since this is the X axis, the problem may be the cable from the control to the carraige. That is most probable. Next would be drive tuning.

George

[JoBwan]

klxrcr,
Just yesterday I had this same problem on a ez-path 1. I found a broken solder where the wire connects to the amphinal connector by the motor. Take a few minutes and open up the amphinal connector to inspect it. It only takes 15 minutes and you may get it fixed without a lot of costs'. I was going to change the motor out, but I had seen this in the past, on a couple of other machines. I'm glad I took the 15 minutes, and re-soldered the connection.

[klxrcr]

Thanks, I'll have to check the wiring out.

Just out of curiosity what does the drive use the tach signal for? can't it determine speed based on encoder feedback?

[machintek]

the tach is for a velocity feedback loop. Yes they could use the encoder but this creates redundancy or safety. Then at a very slow feedrate, you would have to buffer the pulses and they are a square wave. The TC22 did exactly that, eliminating the tach. I cannot tell you why Bridgeport did some of the things they did.

George

[JoBwan]

klxrcr,
Did you find anything with the wiring?

[klxrcr]

I checked it out today, but found nothing, all the pins & connections were good and all wires had continuity. The tach wires, or what I assume to be the tach wires (Xi+ and Xi- on the schematic) both had 0.6 ohms resistance which should be fine, correct? Luckily the wiring diagram was in the enclosure because the manual had nothing....surprise.

So i guess the next step would be drive tuning, I found the trim pots on the drive but they are not labeled and I don't have a scope and I have zero drive tuning experience so that will probably be left up to a tech.

Let me know if anyone has any ideas and thanks for the help so far

[machintek]

Sounds more like a dead short. I thought it was supposed to read closer to 100 ohms.

George

[JoBwan]

klxrcr,
I have seen that new motors are bad from the get go. NOT Very Likely BUT, another thing you might try is this. If you have the old servo motor, see if it is an "SEM" brand. Google search "Clarkson Company" near Chicago. I think it's "clarksonco.com". Steve Clarkson is the ONLY registered SEM service group in the U.S.A. While you can run the machine the way it is, I would send the old motor to him and get it quoted for repair. I've had three motors completely gone thru and the price ranged from $550.00 to $850.00 for total repairs. On two motors he just cleaned the inside for brush dust and found bad encoders and complete inspection of the whole unit. He will only charge for any needed parts and his labor. UPS Red both ways, and I was up and running within 3 days. If this fixes your problem, send the new motor back for warranty, if a warranty applies. If not, you still have a spare motor for either axis on the machine and dig into the problem deeper. It may be worth it in the long run?? Good luck.