On Tuesday 05 July 2016 08:34:15 Rick Lair wrote: > Hello All, > > Figured I would ask here, with all he knowledge of servos and drives > floating around, > > I have been having a problem on another one of our turning centers > where the x axis will "twitch", for lack of a better word, at random > times while moving down ( slant bed, back tool lathe). I have checked > all couplings between the encoder and ball screw, checked the > synchronous belt tension between the ball screw and the servo, I just > replaced the encoder, and I still cannot figure out what my be causing > this. It is not every time it is moving, and it is not in the same > place every time when it does happen. Could there be something funky > going on in the servo? I was thinking if I had a storage oscilloscope > I could what the motor voltage to see what that is doing, but I don't > have one of those, but have flirted with buying one in the past. > > Any thoughts as to what would cause this?
I'm sure you've heard all this before... First thing that comes to mind Rick, is inadequate shielding of the encoder line to the computer. Mine is a single ended circuit, and I forgot to ground the machine frame when I removed the OEM controller and drove the spindle motor direct with one of Jons PWM-Servo modules. That left the machine frame ungrounded and I could find 80 volts of very high frequency noise on it. A lack of a good, stranded copper of at least 12 gauge equ from the frame of the machine to a handy screw near the b.o.b. in the controller is a boo boo. All cables from the controller to the machine going to encoders should have their shielding connected to the controllers common ground at that "handy" screw , but the shields should be cut off short at the encoder to not make a ground loop causing connection. The idea is to first, ground the machine frame via the wire to the controller, so that the grounding resembles a star with all grounds coming from this common point, but no grounds other than that, and with open ends for all shields except at this same common bolt. This ground should be a good connection to the 3rd, round pin here in the US of the power cord feeding the computer and the controller if the machine has no line cord of its own. Ideally, you should be able to lift each of those grounds and then measure a very high resistance or no connection at all from the ground point to the wire lifted. If you find any with a resistance under 100 ohms, that is a ground loop, and it should be run down and the offending ground to wherever removed. Single phase 120 volt machine line cords are a common offender. But in that case I would NOT cut the 3rd pin off the machines cord, but based on the theory that any major shorts are likely to be in the motors etc of the high powered end of all this, I'd still wire it up star style and put the computers power cord, and the controllers power cord on a common 3 wide plug expander, with its 3rd pin cut off thereby putting all grounds in that machines setup on the machines own 3rd pin ground. In the case of my G0704 with no line cord, and powered totally from the electronics box, it has one line cord, feeds the computer full time, and a switch controls the power for the electronics box, which is staged in turning on the spindle power supply only when the 2nd button enabling the machine is enabled. Bringing it all up with 1 switch clears a 25 amp breaker in the service box. Staging it works. Average load when the machine is actually working is 3 to to 9 amps. So now a legal 20 amp breaker suffices. But I digress. The idea being that a major short of something on the machine to the machine frame would go out thru the static ground on the machine, missing the controller and computer so they aren't fried by the short. Cheaper repairs that way... Thats the theory anyway. :) 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> ------------------------------------------------------------------------------ Attend Shape: An AT&T Tech Expo July 15-16. Meet us at AT&T Park in San Francisco, CA to explore cutting-edge tech and listen to tech luminaries present their vision of the future. This family event has something for everyone, including kids. Get more information and register today. http://sdm.link/attshape _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
