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Noise Issues causing all sorts of problems
« on: June 10, 2011, 11:08:54 AM »
I am having what I guess to be noise or interference problems.

Most common is a random "external e stop requested"

however I also get a random resetting of my Z position. That is to say I will home the machine, then as I run the program it (Z readout on the DRO) will suddenly change, and not once has it changed so it didn't drive a tool down into my work.

it has twice changed in the middle of a program while it is running.

Just last night I was trying to carve an intricate logo on to a polished aluminum billet 12x 18 x1. I used the probe to touch off the surface and set my Z .100" higher than the surface and ran an "air cut"

The program ran well was centered. I rewound the program, sent the head to Z 0.000, entered .100 on the DRO, homed the machine  and when I started the run it dove full speed into the face of the aluminum with enough force to spear the bit into the billet and shear the mill head off the mount. After I cut power to the mill head and hit the feed stop, the Z DRO read at -4.6293,

I built my controller from a smooth stepper and Gecko G540.

my limits are optical and I have a 1uf electrolytic already between the ground and supply feeding the limits.

I've set my debounce to 20,000! and I still get the external estop request.

I've completely eliminated my Estop circuit and wired a jumper between my 48V power supply(-Vdc) and pin 10 of the G540.

the 3 internal power supplies have all the negative terminals daisy chained and sent to ground, the earth ground is no where near the chassis ground.

as far as I can tell I have no ground loops ,I build guitars and amplifiers and I am very familiar with ground loops.

I've COMPLETELY removed all 120 VAC wiring from the controller box (mill head and router head power) and re routed them to drop down off the ceiling and at 90degrees to the controller and the wire routing.

the circuit that the controller is powered off of is on its own breaker and has a separate ground rod 12' away from the shops ground rod. The computer, monitor and external hard drive are powered off this too as not to cause a ground loop.

I'm down to two other possible sources:

There is a large 6 bulb fluorescent light fixture maybe 4 feet from the controller .

Maybe the shop power has interference? the power lines  run under high tension lines about a mile up the road. I'm VERY rural and am the last house on this grid with the the last pole sitting in front of the driveway and the power lines terminate on it.

I am at my witts end here.


Ray





« Last Edit: June 10, 2011, 11:21:21 AM by Lemic »
Re: Noise Issues causing all sorts of problems
« Reply #1 on: June 10, 2011, 12:37:04 PM »
both my cnc mills share the same cabinat and it is a super noisy area. we had a hell of a time to get it up and running. now i just have to see if it will be stable.

we used all kinds of caps and pull up things that are way out of my pay level.
Re: Noise Issues causing all sorts of problems
« Reply #2 on: June 10, 2011, 12:40:24 PM »
First thing I'd do is eliminate the Smooth Stepper and go to PP.  If I recall, when we tried the SS, we had similar issues where axes would sort of take on a mind of their own now and then.  The SS is USB and USB is sensitive to noise.  Also make sure that any relays or inductive loads have a snubber across their coil terminals.  A spike from a relay coil can cause strange things also.
Re: Noise Issues causing all sorts of problems
« Reply #3 on: June 10, 2011, 01:20:20 PM »
thanks guys for the support.

rrc1962,

I'm leaning towards removing the Smooth stepper also, can you recommend a breakout board that is compatible with the G540?

or is it even necessary?

OH!, I was careful to not use relays, only solid state relays.
Re: Noise Issues causing all sorts of problems
« Reply #4 on: June 10, 2011, 01:42:04 PM »
G540 has the PP interface built in.  It doesn't need a BB.  Just connect it directly to your PC.  G540 is a very nice unit.  We've had zero problems with them.