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Motoman robot - small servo erratic at slower speeds

Milacron

Administrator
Staff member
Joined
Dec 15, 2000
Location
SC, USA
Late 1980's vintage Yaskawa Minertia, 5th axis servo runs fine at the faster speeds but at slow speeds it either turns in "steps" or not at all (this, under no load with motor removed) Brushes have plenty of length, everything very clean, no oil or dirt anywhere. Cap on rear end contains optical encoder.

With power removed, nearly impossible to turn by hand...is that the way it should be ? (but when turned with wrench it feels smooth...just surprisingly difficult to turn)

yaskawa1.jpg


Weight is 7.5 lbs
 
Yellow and red wires a brake perchance? On when power off?
Could be I suppose but the 6th axis seems to use a smaller version of the same motor and it turns easily by hand...but then maybe it has a brake too and the brake isn't working...hard to say at this point... guess I'll just have to dissassemble the little bugger...
 
On my mid-80's Mazak's lathes, with dc servos, the x-axis has a brake to prevent the turret from dropping down the slanted carriage with the power off. The brake itself must have power to release, and is always released when the machine is on.

A sticking/bad brake would be my guess.
 
Fixed it. Turns out there was a brake and the brake wasn't releasing. But not because there was something wrong with the brake...rather, there was no voltage getting to it. Still don't know why that was exactly but further investigation revealed all axis receive 24 volts to their brakes when the servo paks are turned on, since, once the servo power is on all non moving axis are held in position electronically anyway. The brakes are only to retain axis position when the power is off. So I just spliced the 5th axis brake wires into the 4th axis brake wires and all is well.
 








 
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