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Offline Tarak

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G31 alternative
« on: August 13, 2016, 06:54:20 PM »
Because of some of the strange issues I am having with G31, is there any alternative probing function to use instead of G31?
I am writing a probing routine that is fairly standard, but occasionally when it runs a line like "G31 Z-5. F100", the A axis will rotate as well????
But the next time I run the code it may not rotate??????
It's a very strange issue, has anyone experienced anything like this?

Tarak

Offline Tarak

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Re: G31 alternative
« Reply #1 on: August 13, 2016, 09:42:11 PM »
Sorry I should of mentioned, I am using Mach3 with a Ethernet Smooth Stepper (I'm starting to wonder if the ESS could be the issue)

Offline Tweakie.CNC

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Re: G31 alternative
« Reply #2 on: August 14, 2016, 03:19:52 AM »
The problem does relate to the ESS and it is believed to be caused by electrical noise. This same issue was discussed on the Warp9 forum a little while back in this thread
http://www.warp9td.com/index.php/kunena/7-general-discussion/5484-ess-mach3-g95-g32-g76-problem?limitstart=0

Tweakie.
KEEP SAFE !
Re: G31 alternative
« Reply #3 on: August 14, 2016, 04:05:23 AM »
Probing is unfortunately a motion controller function (which is why some buyers of far eastern motion controllers in their early days of cnc become disappointed later when realising some motion controller functions do not work at all or as intended),

That being said, m3 can be unpredictable and occasionally do something unexpected....

One place to look (before something other than m3 + ess) may be the probe it's self, or its wiring arrangement, is everything running off the same electrically supply, is it maybe because when the touch probe touches the object, the ground or vcc is all of a sudden causing a spike via other ground connection (motors, prox sensors, grounded table etc) back to the ess

One suggestion may be to run the probe off a small battery supply, via an optoisolator/ optocoupler then into the probe input of the ess.... hence no chance of shared ground or vcc connection....

Hence check your wiring and circuits being formed
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline Tarak

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Re: G31 alternative
« Reply #4 on: August 15, 2016, 12:15:13 AM »
Thanks Tweakie.CNC and robertspark, I was wondering about something like this, it's just such a random issue.
I was going to check the probe wiring, but then I realised it's doing all the weird behaviour before the probe even touches the part.

I am going to try a good old fashioned parallel port controller card, I think I have an old one around here somewhere.
I will let you know how I go.
Re: G31 alternative
« Reply #5 on: August 21, 2016, 03:24:06 AM »
Hi All,
very interested it Rob's comment about the probe setup.

I have an issue with my machine which doesn't prevent me using it but is a
concern.

I use Vexta 5phase steppers and I would swear one or more of them are leaking
to earth. The frame of the machine is earthed via the spindle earth. At one
stage I had the spindle dismounted and lo and behold the frame of the machine
goes to about 130V!!! Yeah, that's correct 130V.

I fitted an earth wire back to the common point in the controller box and measured
30mA return current. I did an insulation test on each of the steppers with the drive
disconnected with a 500V tester, no problems. But the fault is definitely in the stepper/
drive arrangement because when you depower the drives the fault disappears and yet
no leakage from the steppers???

The Vexta drivers I use produce around 130V at the DC link so its related somehow.
Vexta is really good quality Japanese gear and having paid thru the nose for it don't
want them to be faulty but what other conclusion can I come to? Even worse is that
the steppers and low (3 arc min) backlash planetaries work like real troopers. They
maintain good torque right up to 2400rpm. At cutting speeds the thrust they and
the gearbox produce is formidable, 1500lbf, and these are 23 size. I refuse to throw
them away, they are just too damn good!

My best guess is the dreaded 'homopolar' current, which according to Kirchoffs laws shouldn't
be. Then again I don't think Kirchoff ever published anything about CNC! Two hundred years
or so before his time... but still.

When I made a probe circuit I certainly didn't want any mystery currents flowing back into the
BOB/controller so I made an opto-isolated probe. Additionally I put a bridge circuit in the open
collector lead so that the hook-up to the BOB is polarity insensitive. It raises the low output voltage
to about 1.5V but my BOB has no trouble with it. Really simple and fits battery and all into a little
plastic cup a bit bigger than an eggcup and worked flawlessly from the start.

Craig
My wife left with my best friend...
     and I miss him!

Offline Tweakie.CNC

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Re: G31 alternative
« Reply #6 on: August 21, 2016, 04:24:15 AM »
Craig,

As you say the motors all pass the insulation test but I would be very concerned about measuring a current as high as 30mA between the machine frame and Earth.

Tweakie.
KEEP SAFE !

Offline Davek0974

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Re: G31 alternative
« Reply #7 on: August 21, 2016, 04:26:21 AM »
Can you not bring the electrical stuff on bit by bit and measure the leakage at each stage?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.
Re: G31 alternative
« Reply #8 on: August 21, 2016, 04:26:50 AM »
Don't carry out an insulation test on anything electronic!

Test the wiring, but don't test the device.  Doing a 500 volt DC test on a device not rated for 500v is a sure way to end up with problems in my opinion (being a young spark (electrician) many years ago I tested a lighting circuit only to kill a whole load of electronic lighting ballasts).

Earthing and providing a means of earth differs around the world by locality, and it can be a very emotive issue with everyone believing they, the system they learnt, or that in their locality is right.  

However... a basic rule remains.... if the device is wired up with live and neutral (or hot wire to hot wire), the leakage to the casing or earth point should be zero.... or you have a problem.

30mA is a high leakage current, and I'd suggest in plugging each of your drives and motors, testing the wiring, and then plugging each of the drives and motors in in turn to establish which drive and motor has the leakage issue.  If you need to swap the drives and motors around to establish which drive or driver is creating the problem exactly, then I'd suggest doing that.

I'd suggest running a gcode file which tests just that one axis motion at full rapid movement.... such as g0 x100, g0 x0 back and forth....id open up Microsoft excel and drag 150 lines of g0 motion, and copy and paste it into a tap file.  So it will give you time to test the machines leakage.

I suspect you have a wiring problem (note I've not seen your machine, don't shoot the cnc messenger!)... I'd suggest that somewhere the wiring is getting mixed up with ground, 0volt or something like that.

I'd suggest stop for a moment (as I know this can be emotive), and just reconsider all of the circuits in your machine, as they need to be wired relative to each other because of the way that they manipulate voltages

Start at the electrical supply... you have two main wires (forget about earth for a moment as some parts of the world use one of the hot wires as earth as its also the grounded neutral point, instead of the centre tap neutral which seem to be the way it's done in to US for domestic supplies (nomenclature different, outcome the same)

These two wires will be wires up to your low voltage supplies one for the 5v, 24v and another for your drives.

The output of these (however many you have and whatever their voltages) are relative to the two output wires... do not at any point connect these to the earth terminal, even if they say zero volt (0v)

These lower voltage power supplies are then connected to your motion controller, and break out boards, and spindle and drives.... some of these have outputs... such as the motor drives... take the wires out of these and wire them direct to the motors... at no point should any of these output wires be connected to the earth point, casing, frame etc, even if they say GND or 0V.

Same thing with bob sensors....

Now, at this point your earth is wired, and it is basically only connected to the casing of each device, or a dedicated terminal that says earth...

Be very careful when the device says "GND" as it may not actually be the earthing point.... test it with a voltmeter set on ohms or diode beep test between the terminal and the casing.

Only this casing earth hours back to your incoming electrical supply earth.

Sorry for the long post

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: G31 alternative
« Reply #9 on: August 21, 2016, 04:33:47 AM »
Whilst I look for my tin hat and sand bags...

However... a basic rule remains.... if the device is wired up with live and neutral (or hot wire to hot wire), the leakage to the casing or earth point should be zero.... or you have a problem.

Please note that with motors, it is possible to obviously get an induced leakage current, by the very nature of their operation of generating a magnetic field... more so with steppers and servos because the frequency their supply switches is much much higher than your run of the mill electrical supply appliances at 50 or 60hz supply voltage....

But 30mA leakage is still very high for an induced leakage imho.

Rob
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”