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SQT 250 MS overload on startup (intermittent)

sasky115

Plastic
Joined
Mar 21, 2022
I recently started having this problem on my 1998 SQT 250 MS (T Plus) where sometimes when moving the X axis for the first time after startup it throws an overload alarm - even when moving as slowly as possible. Sometimes it does it before the machine even turns on completely, sometimes it doesn't do it at all.

Brake seems to work fine - you can unplug it from the board and hear it click and you can also see the turret drop a bit before the brake catches it when overload is triggered.

Sometimes you can hear the motor grumbling like it's struggling or maybe doing very small corrections. If you can slowly move the axis and get past this stage the machine then works fine all day. The load meter doesn't increase gradually before this happens. You can move in 0.001 mm increments and hit a spot where the motor just starts doing it and the load meter starts jumping all over the place, then you move by 0.001 mm and it stops. At rest, it usually shows 55%, after an overload and restart it goes to 33% so that's suspicious. It used to always be at around 55% (is that a bit high?).

After the overload is triggered the X axis position sometimes (I promise this is the last 'sometimes':crazy:) jumps by about 1mm randomly - that doesn't look normal either.

A Mazak tech came out, swapped X and Z drives - still the same. He's coming back next week and I'd like to find some suggestions as to what may be causing this. The most frustrating part is that it only does it after the fist startup and even then not every time. Any suggestions will be greatly appreciated.
 
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noname777

Hot Rolled
Joined
Aug 24, 2018
Location
NSW , Australia
swap Z and X axis encoders. Check servo diagnostic page see if they are the same. Both should be OSE and whatever number follows.

Worse case scenario but you don't want to think about it is X axis servo motor rotor is demagnetized and behaves abnormally.
 

sasky115

Plastic
Joined
Mar 21, 2022
Thank you, we will try swapping the encoders on Thursday.
What's crazy is if it gets past the first move along X it just works all day after that.

Here you can see (and hear) it start when I reach X244.46

Here it can be heard better

And the X coordinate jumping after overload
 

sasky115

Plastic
Joined
Mar 21, 2022
I'm suspecting the encoder as well, I will try if it's any different on other turret positions.
 

noname777

Hot Rolled
Joined
Aug 24, 2018
Location
NSW , Australia
unbelievable that Mitsubishi is still making money making those OSE and OSA encoders. 20 years old development and yet still brings jobs and profit to Japan ;)

next time u would be better off if you go to DIAGNOSTIC screen and look and CYCCOUNT data to see actual digits coming from encoder while manually moving axis somewhere. POSITION page says nothing at all when it comes to servo diagnostic. My bad I didn't mention it before
 
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sasky115

Plastic
Joined
Mar 21, 2022
In my case they won't be making much money except if the refurbished encoder I ordered doesn't work:scratchchin:. Thanks for the diagnostics tip, I'll add it to my troubleshooting folder, on a machine this old I may need it again soon:crazy:
 








 
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