On Wednesday 03 August 2016 10:23:43 Leonardo Marsaglia wrote: > I'll take a look at the PCBs to see the caps and how they look like. I > should note that this happens on days with high ambient humidity like > 85% and more. I have some silica gel bags inside the cabinet, I don't > know if they really help but sure they don't hurt. Anyway these drives > are from the early 80's so I'm more than ready to expect a failure in > any time, but I hope they to last a couple of years more. > > In any case I'm planning to buy new DC servo drives sometime soon. I'm > looking for the AMC drives as Sam on this list once told they used > them for a Mazak. There are also the ones from Granite Devices from > finland, fairly cheap. > > What I would like to measure is the real power consumption because in > the manuals It says the Z servo has something like 1.2 Kw and the X > servo 0.9 Kw (My concerns is, is this a normal power output for servos > on a 1 meter between centers lathe?). I'm affraid that may be the > numbers are for another Mazak smaller than this QT20 although the > manual says QT20. Or is it that with ballscrews the power needed is > quite low compared to what one could be used to with normal screws and > brass nuts? Sorry for the little OT. > > Leonardo.
Servo's, generally speaking, will use only the power it takes to accomplish the job. Ball screws, for horizontally moveing loads, will use 1/4 or less of the power it would take to do the same job with good acme bolts & bronze nuts, and because of the relatively coarse tpi, will move it farther and faster. Holding a vertical load, like the knee of a big mill, will use power while stationary just to hold up the weight of the knee which can be a considerable amount of power. Since the knee doesn't normally get moved all that fast, I'd give a bigger stepper a chance at that job, as its possible that its power off magnetic detent may be sufficient to hold position when powered down. With acme bolts and bronze nuts in the knee, the unwind to the bottom stop when powered down is not a problem, but winding it back upward will take a bigger motor. I can visualize a fixed at the base ball screw for a heavy knee, with a ball nut on it, being turned by a worm gear, with a ball bearing thrust washer on top of the nut, the worm being turned by a more normally sized servo and profile the PID for a very small overshoot, half a thou max. That overshoot would put the servo in a resting position where the worm would carry the weight and the motor is essentially doing nothing. That same profile, going downward, would overshoot and the servo would need to lift it, essentially repeating the lift profile, and once again the worm friction against the bull gear should balance out with the worm gear to bull gear friction doing all the holding work. My HF micromill has had a belt driven set of bronze nuts for the z drive these days, with those nuts supported by large AC ball bearings, uses a 1/2" 10 tpi screw solidly planted into the head casting. The moving of that drive screw from behind the post where all it did was bind up the short ways when it pushed down like to drill a hole, with a 262oz nema 23 motor on it, could only put 5 lbs on the scales. Moving the 20 tpi screw to the front of the post and making it a 10 tpi screw, it measured 150 lbs on the drill bit tip when the motor cogged. It still has other problems related to the short "wheelbase" of those ways, so it now has 4 ball bearings on brackets that ride the face of the post, increasing the heads wheelbase to around 6". That and good lubrication of the post has controlled the stiction good enough to give me .001" accuracy. So other than a higher voltage motor supply (from 28 to 42) and a 5i25 card, little else will be done to that machine as its otherwise working well. > 2016-08-02 20:54 GMT-03:00 Gene Heskett <[email protected]>: > > That might well be Leonardo's problem too. High humidity might be > > electrical leakage caused by the leakage products on the pcb from a > > failed cap, so while I am not as positive in Leonardo's case, its a > > possibility that should cause it to be visually inspected for such > > leakage. Its generally white, looking a bit like dried pancake > > batter. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
