Messages

1001

FAQs / Re: Losing steps or something?

« on: November 02, 2010, 05:41:15 AM »

It was what you mentioned before. The drive was expecting the direction pulse to appear on the falling edge of the step pulse but the BOB/Smooth Stepper combination was outputting it on the rising edge (or vice versa).

A question here. In the past I have always used the Dir line as a 'state' rather than as a pulse. That is, Hi goes CW, Low goes CCW. Does this apply here? Surely?
Otherwise, a timing problem with the transitions. Yuk! Sounds horribly right.

It was only after I accidentally removed both the SS and the BOB from the sequence that I found the problem was gone. A new SS plugin cured the problem.

Are you say then that either the SS or the BoB are apparently altering the timing of the original signal ? Oh Dear.

Cheers

1002

FAQs / Re: Losing steps or something?

« on: November 02, 2010, 03:21:06 AM »

The reason I doubt it is Mach, is that there are many machines running Mach3 on daily basis producing thousands of precision parts. These people would have easily noted a problem like this if it existed.

I am willing to believe, but it is certainly weird!
But if someone is making thousands of parts, I would imagine they would be using an jigs and autoloading of pallets, and under these circumstances just maybe they are also using a touch probe to check each pallet? Dunno, but maybe.

Software bug or hardware issue or a combination of both, I think it is something unique to Don's setup that exposes the problem.

Not arguing at all, but he has swapped so many of the components over. What's left?
Hum - clean XML file?

I have had exactly the same problem of losing steps on reversals, but I was able to isolate it to a combination of the BOB and SS plugin I was using.

Details, please! What was going wrong, and how did you fix it? The info may help here.

The test I was running was set to incremental jog mode and the finest increment I could read with a DTI (0.01mm), then use the keyboard to step jog one direction and the other repeatedly. I could actually see the DTI needle moving gradually to one side. After the problem was resolved, the DTI was spot on after hundreds of iterations.

A neat method. Worth trying here maybe.

Don, the stuttering you're seeing is not something normal.

100% agree. Need to sort it out. High probability of it being responsible. I do NOT get stuttering!

Cheers

1003

FAQs / Re: Losing steps or something?

« on: November 01, 2010, 05:10:15 PM »

Obviously the signals to the driver are corrupted.  The drivers only send the motors where they are told.

Yep.

Considering that the base program I'm running is in the Mach manual, it would seem that if it were a common problem, everyone would see it.  It is not subtle if you are checking repeatability.

Ah, but how many have actually done the sort of testing you are doing? NOT MANY!

I did notice that when running the test with G1X+.005 the machine stutters near the beginning of the test about 3 times and then runs smoothly for the remaining 2/3 to 3/4 of the test.  the BOB activity LED flickers accordingly.

OH???
Now that is interesting! And it looks like a software issue.
I've spent 40+ years writing software. Bugs happen, even in commercial products. (Windows, anyone?) Why not in Mach?

Cheers

1004

FAQs / Re: Losing steps or something?

« on: November 01, 2010, 06:03:37 AM »

I did, however, get the Larken Viper 200 servo drive and Ametek motor with a 500 line (2000 count) encoder hooked up.  It only accepts +5V common signals, so I had to use the PMDX breakout board.  I put an index mark on the sproket that is on this motor and an indicator so I can see if it offsets.  Yup.  It seems to be doing the same things the stepper system does.

Getting harder to say the problem is random noise, isn't it?
Ahhhh... was the motor hooked up to the hardware, or just sitting bare? This affects the acceleration tuning etc.

Curiosity...  OCX driver test - what should I be looking for when running it.  It had very small vertical lines in the graphical display when I ran it when I put the computer into service... 

Mine does too.

Cheers

1005

FAQs / Re: Losing steps or something?

« on: November 01, 2010, 01:39:01 AM »

X+.001 buzzes but does not offset.  sound has 9 pulsed and then smooth buzzing...  I ran this multiple times with no offsetting.
X+.00015 machine walks right over to -.055". Aargh!
X+.010 table jiggles like a paint shaker and offsets - get this! - -.050".

Some of the results are consistent with the idea of a bug at the change of direction. However, this buzzing puzzles the hell out of me. Jiggling like a paint shaker ... ? That's really weird!
Thing is, until we can explain everything, we do not know what is going on.

Hum - I don't suppose you can find a digital storage CRO and LOOK at the signals by any chance?

Can I suggest ... putting a pause between each reversal. Yes, that will make the program much slower, but it should let the first motion stop before the second (reverse) motion starts.
Alternately, do you have Mach in Constant Velocity mode? If so, switch to Exact Stop.  (Ho hum - or vice versa...)

Running experiments is all very well, but they can be bewildering if you don't have a theory to test. (Sorry about the preaching: my background is a PhD in Physics.) We seem to have some consistency with the number of cycles and the offset, and some consistency with the idea of very small increments producing variable results, so what's the buzzing? Is it that the acceleration parameters are just not handling the mass of the table when you combine very small steps with frequent reversals? Or is there a slight overshoot making the Geckos get very shirty about the reversal? Hence the pause idea.

Cheers

1006

FAQs / Re: Losing steps or something?

« on: October 31, 2010, 07:42:39 PM »

Thanks for the help so far.  Don

Hey, if the effect is real, I want to know - and to see it fixed! Very selfish motives ... :-)

Cheers

1007

FAQs / Re: Losing steps or something?

« on: October 31, 2010, 05:46:04 PM »

I just ran some more tests. Changing line 5 from G1x+.1 to G1x-.1 does not change the direction of the offset.  it still moves +.
+.005 in 50 repetitions.
+.010 in 100 reps.

That is consistent.

I set the line 5 to read G1X+.00005 and ran the program with the loop set for 100 reps.  No movement was detected at all.  None!.

This is not inconsistent at all. Such a small change may simply leave the Step signal in the opposite state, such that flipping the Dir line does not cause the change in the Step line. In effect, this is working around the bug (if I am right).

I set the line 5 for X+.00010 and 100 reps yields +.010 offset.
Set for x-.00010 yields the same +.010 offset.  Hmmm.

Consistent. But try 150 and 200 cycles as well for really convincing proof.

Now for the wierd one.
I set the line 5 to read G1X+.00015 and ran the 100 reps.  the offset looked like almost .0110"!!!
So I ran it again and again - a total of 10 times.  Offset is .110 total.

Ok, two parts. The first part is that going from 100 cycles to 1,000 cycles gives 10 time the error. This is entirely consistent with the idea of a bug somewhere, either in Mach3 or in the Mach3/Gecko interaction.
What significance there is to the fact that you are micro-stepping the Geckos is something I am not entirely sure about. It may be worth while asking Gecko about this as well - with full data.

When it runs the program, the movement sounds sort of stuttery, unlike when it is actually moving some distance. 

Dunno. Obviously you are way down in the acceleration phase, and that could be tricky. I would check this with both ArtSoft and Gecko.

Bottom line: while cleaning up the earthing etc is good, I do NOT think the real problem lies with your hardware. It is in the ArtSoft and/or Gecko domains. You may be able to produce evidence of the problem, but I do not think you can resolve it yourself.

Cheers

1008

FAQs / Re: Losing steps or something?

« on: October 31, 2010, 04:44:15 PM »

Single step resolution of the machine is theoretically .00005"  of course the mechanicals aren't that precise.  My tests of "backlash" have shown about .0003" or so.

One pulse at each reversal gives 2*0.00005" = 0.0001" per cycle. As predicted.

Each cycle seems to move the offset .0001".  Only by raising the number of iterations can I see it on my machine dials which are calibrated in .001" increments.  If I run the loop 50 times, I get .005 past zero. 100 times, I get .010 past zero.  etc.

If this applies to 150 iterations and 200 iterations, we have a software bug - or a strange interaction between Mach3 and Gecko. I favour the plain SW bug.

Document fully and report to ArtSoft.

Cheers

1009

FAQs / Re: Losing steps or something?

« on: October 29, 2010, 04:44:37 PM »

OK, so even with just one axis hooked up you are seeing the creep. I make the creep 0.0001" per cycle, right? Just possibly that is the resolution of your axis?

I am now 99% convinced that this is a bug in how Mach handles multi-axis moves, at least with the Gecko drives. Changing the Dir signal is causing a change in the state of the Step signal which is effectively injecting a single step. The consistency of your results precludes random noise imho.

Checks to run:
1) Verify that this produces the same amount of creep despite having moves of 0.25", 0.5" 0.75"...
2) Verify that N cycles produces a creep of N*0.0001", where N=50, 100, 150, 200 ...
3) Check to see what the single step resolution of your machine is.

If both of these produce positive results, then you have a good case for going to ArtSoft with the data and requesting a check of the code.

A further rather cunning test is as follows, and it assumes that your resolution is 0.0001". Repeat the 50 cycle test for 1.0000", 1.0001", 1.0002" ... See if there is any variation in the creep as you move through the single-step increments. What you will be trying to do here is to alter the state of the Step signal when Dir is flipped. This may or may not produce interesting results - hard to say at this stage.

Making your wiring really clean is worth doing of course, but it seems you really have two separate issues here.

cheers

1010

FAQs / Re: Losing steps or something?

« on: October 26, 2010, 05:21:53 AM »

I removed the temporary earth strap, but there is still continuity from the Cap to chassis.  I don't know where.

OH?? As Tweakie said, pursue this one. It might be rewarding.

>

According to the manual the breakout board AND the Geckos both use optical isolation. 

Nice. And good.

Cheers