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Skipping movements intermettently, & work offsets
« on: September 27, 2011, 05:22:38 PM »
When engraving identification letters on various components the machine is sometimes missing part of the movements, giving rise to various problems. Here is the latest programme to give problems:

G90
G0  X121.0 Y-75.0 Z0.0 M3
    Z-32.5
F   200
G91
G0  x -1.75
G51 X0.7 Y0.7
M98 P066

G50
G90
G0  Z0.0
G0  X0.0 Y0.0 Z0.0
M30

O066  (upper case B)
G91
G0  Y0.500
G1  Z-2.00
    X2.50
G3  X0.00 Y4.00  I0.00 J2.00
G1  X-2.5
    Y-9.00
    X2.50
G3  X0.00 Y5.00 I0.00 J2.50
G0  Z2.00
    X5.50 Y-0.5
M99

The sub-routine is from a library of alphabetic characters used with different engraving jobs. The G51 scales it from 10 mm high to 7 mm.

The B starts with the middle bar, then the upper curve, horizontal to the left, down the main upright, horizontally across the base then up with the lower curve to complete the letter in one continuous cut.

Today, two times out of four, the first curve of the B was not completed so the remaining lines were out of position, maybe 1.5 mm right and 0.5 mm down, so the upright is displaced to the right and the end of the line does not meet the middle bar as it should. This has wrecked the job at the last operation, which is very annoying.

At an earlier stage in developing the interface to this machine I got crosstalk between the watchdog signal and the X axis drive in a short section of ribbon cable used to extend the parallel cable into the machine. This gave rise to un-programmed moves on the X axis. Getting rid of the ribbon cable and taking the printer lead direct to the interface board seems to have solved that one, but it might be relevant. I still suspect the quality of printer cables when used for machine control.

Another programme on the same machine but using a different setup profile resulted on one occasion in the last character being out of position, showing that one rapid move had missed the X Y moves, and a second time the last character was overwritten on the second last, and the cutter dug in deep indicating an entire rapid move had been missed. Programme (without all the subroutines) below:

G90
G0  X1.0 Y-75.0 Z0.0 A-121.0 M3
    Z-32.5
F   200
G91
G0  Y2.50
G51 X0.3 Y0.3
M98 P050
M98 P046
M98 P048
M98 P032
M98 P109
M98 P109
M98 P032
M98 P083
M98 P084
M98 P065
M98 P073
M98 P078
M98 P076
M98 P069
M98 P083
M98 P083
M98 P032
M98 P083
M98 P084
M98 P069
M98 P069
M98 P076
M98 P032
M98 P040
M98 P051
M98 P049
M98 P054
M98 P041
M98 P032
M98 P067
M98 P069
M98 P082
M98 P084
M98 P046
M98 P032
M98 P050
M98 P056
M98 P051
M98 P051
M98 P052
M98 P054



G90
G50

G0  X0.0 Y-78.0 Z0.0 A-121.0
    Z-32.5
G91
G51 X0.3 Y0.30
M98 P083
M98 P078
M98 P066
M98 P032
M98 P069
M98 P108
M98 P101
M98 P099
M98 P116
M98 P114
M98 P111
M98 P110
M98 P105
M98 P099
M98 P032
M98 P083
M98 P101
M98 P114
M98 P118
M98 P105
M98 P099
M98 P101
M98 P115
M98 P032
M98 P050
M98 P052
M98 P072
M98 P114
M98 P032
M98 P084
M98 P101
M98 P108
M98 P032
M98 P048
M98 P055
M98 P055
M98 P049
M98 P048
M98 P056
M98 P052
M98 P048
M98 P051
M98 P054
M98 P049


G50
G90
G0  Z0.0
G0  X0.0 Y0.0 Z0.0
M30

O049  (numeral 1)
G91
G0  Y2.50
G1  Z-2.0
    X2.00 Y2.00
    Y-9.0
G0  Z2.00
    X5.00 Y4.50
M99

O054  (numeral 6)
G91
G0  X3.00 Y4.50
G1  Z-2.0
G3  X-3.0 Y-4.0 I1.1667 J-4.0
G1  Y-3.0
G3  X4.00 Y0.00 I2.00 J0.00
G1  Y1.25
G3  X-1.75 Y1.75 I-1.75 J0.00
G1  X-2.25
G0  Z2.0
    X7.00 Y-0.5
M99

Two lines of text are written using X Y scaling to set the character height, with a non-scaled move between lines to set the line spacing and centring.

I've only included the last two character subs - 61 - as that's where the problems occurred. Most of the subs have been used successfully in various combinations, so I don't think there is anything wrong with them in principle, although one or two may have errors in them. I would say the last G0 in sub 049 was being missed.

The only hint I can find, and it may not be relevant, is that I can't get the axes to zero when I issue G28.1. The initialising code at switch on is G28.1 X0 Y0 Z0 A0. This usually leaves X at 3.44, Y at 2.55, not at zero. If I look at the offsets, G54 Is also at X 3.44, Y at 2.55. If I zero them in G54, then the Machine Coordinates change from all zero to X3.44, Y 2.55. If I zero the machine coordinates the values reappear in the G54 offsets.

How do I, once and for all, make all coordinates zero when the machine has homed and (officially) zeroed all axes? My suspicion is that this discrepancy is giving rise to movement errors, but I can't prove it.

The computer is a VIA ITX running windows XP, configured by Les Caine as "Mach in a box", using Mach R3.042.020, and with his interface card. Motor drivers are IM483.

Can anyone shed any light on the missing movements, the zeroing problem, and any possible link between them?




Keith  S. Angus

Offline BR549

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Re: Skipping movements intermettently, & work offsets
« Reply #1 on: September 27, 2011, 09:31:22 PM »
The code runs fine here so it is not the code. Mach3 in NOT know to miss run Gcode. SO that leaves the machine . It is occasionally missing steps for some reason.

As to the G28.1 it should move to the home switches back off and set machine zero to X0 Y0 Z0. That is machine zero NOT work zero. The only way those 2 would be the same is IF you setup the Home offset to reflect the difference OR the home switches are setup AT work zero as well. THEN machine zero and home zero would be the same.

BUT if you then setup any work offsets such as  ZERO the XYZ then the WorkZero changes via the fixture offsets and you will see the change in the  fixture offset values.


CLear as MUD???, (;-)
Re: Skipping movements intermettently, & work offsets
« Reply #2 on: September 27, 2011, 11:03:30 PM »
Thanks for looking and testing. I reckon the code is OK as I'm running batches of parts and using the subroutines in different orders for the various names and descriptions that get engraved. So the letter B  has only given problems in the first example although it is called up in the second one.

As for the zeroes, in one setup the G28.1 zeroes everything, which is what I need. The components are in a single fixture and it is essential that the home position is the programme zero. There is no other datum. So why does G54 have these residual values? I never put them there, and with a different profile on the same machine they are all zero. (I run different profiles depending on whether the machine is running a rotary job or working on the flat.)

It wouldn't matter too much but after months of experiment and discussion the salesman has gone mad and the orders are coming in, and now the problems show up, and I'm busy on other projects. So everything's quite normal!
Keith  S. Angus
Re: Skipping movements intermettently, & work offsets
« Reply #3 on: September 28, 2011, 12:23:10 AM »
Hmmmmm......  I wonder if this is related to the problem Brian and I have been fighting for the last week.  I've got a couple of programs that will, occasionally, cause Mach3 to spontaneously change the machine coordinates for one or more axes!  I can induce the problem with some regularity here, while Brian has only seen it once (just today!).  However, this is running with a SmoothStepper, and we suspect this is the result of a synchronization issue between Mach3 and the SS, though we can't prove it.  What I see, quite consistently, is one or more axes will "freeze" momentarily when the offsets get whacked.  After than, the program continues to run, but, of course, the machine is no longer where it's supposed to be, because Machine Zero has been shifted.

Another problem I've seen that could be relevent is that under some, as yet undetermined, circumstances, it appears Mach3 is violating acceleration limits.  I have a test program that runs perfectly doing all moves as 50 IPM G1, or doing all the moves as 200 IPM rapids.  But, do the moves as 100 IPM G1s, and the servos fault all over the place (and the ONLY time I've EVER seen my servos fault is when I've crashed the machine HARD, so this is NOT a machine problem).  Since your machine is (I think) stepper-driven, if the acceleration limit is not being respected, it is entirely possible the motors will not move at all at times.

Regards,
Ray L.
Regards,
Ray L.
Re: Skipping movements intermettently, & work offsets
« Reply #4 on: September 28, 2011, 08:06:04 AM »
Yes, it's all on steppers, with no form of feedback. The acceleration profiles have worked well before, and the speed is not high - I haven't got around to speeding the machine up yet.

I've seen missing or added steps before, and they give a random result. I'm suspicious of Mach3 because this fault misses movements. Writing the letter B the first arc is not completed, with the same result two times, which would not happen just by chance, and no fault two times. In the second example one or more components - X, Y, or Z of a rapid command were missed. This is not the same as a few steps.

When i get back to the machine I will try repeated Bs to see if there is a pattern. I think the graphic screen was showing a discrepancy too, which would definitely be the programme, but when I zoom in on it to get the detail, the cut path vanishes. I must start with the image zoomed, and see what happens.

When I start up on one profile the machine zero is at the machine home, but on the second profile, made from the first with mods for three axes instead of four, the machine zero is different and the Y axis, which was not changed, hits the end stop when zeroing, which it never did before.

It's all very puzzling, and the parts are due out tomorrow!
Keith  S. Angus
Re: Skipping movements intermettently, & work offsets
« Reply #5 on: September 28, 2011, 08:20:43 AM »
First, if you accelerate a stepper beyond its capability, you will not generally lose one, or a few, steps.  It is entirely possible for an entire move to "disappear".  Once you exceed the motors capability to accelerate, the motor will stall, and just sit there buzzing.

"When I start up on one profile the machine zero is at the machine home, but on the second profile, made from the first with mods for three axes instead of four, the machine zero is different and the Y axis, which was not changed, hits the end stop when zeroing, which it never did before." - Now this does sound like exactly the problem Brian and I are chasing right now - the Machine Position DROs are getting changed spontaneously.  In my case, I set the Z axis Machine Zero to the top of my quill travel.  But, after the fault occurs, I will find that at that same physical machine position, the Z Machine Position DRO will instead read +0.500" or more.

When the "B"s are incorrect, are they *always* incorrect in the same way?  i.e. - Is it always the same segments that are missing?

Regards,
Ray L.

Regards,
Ray L.
Re: Skipping movements intermettently, & work offsets
« Reply #6 on: September 28, 2011, 08:34:22 AM »
Well, the problem with the Bs has only happened twice out of four attempts, but yes, it was the same both times. That's as judged by two skilled pairs of eyes, not measured. The other fault occurred on the same rapid move both times, the first time losing the Y, the second time losing X,Y & Z. I will have to look closely to see what happens to the DROs. I want to run the B cycle whilst watching the screen, not the cutter, but I can't get to the engraver at the moment. At least I can cut fresh air instead of wasting components.
Keith  S. Angus
Re: Skipping movements intermettently, & work offsets
« Reply #7 on: September 28, 2011, 09:07:23 AM »
Well, the problem with the Bs has only happened twice out of four attempts, but yes, it was the same both times. That's as judged by two skilled pairs of eyes, not measured. The other fault occurred on the same rapid move both times, the first time losing the Y, the second time losing X,Y & Z. I will have to look closely to see what happens to the DROs. I want to run the B cycle whilst watching the screen, not the cutter, but I can't get to the engraver at the moment. At least I can cut fresh air instead of wasting components.

Please look at both machine position and work position after it screws up again.  If it's the problem I'm seeing, the offset between the two will remain correct, but the machine position will have shifted away from the physical machine home position.  This shift may occur on one, several, or all axes.

Regards,
Ray L.
Regards,
Ray L.
Re: Skipping movements intermettently, & work offsets
« Reply #8 on: September 28, 2011, 06:49:05 PM »
I had about an hour this afternoon to play with the machine, and came away even more puzzled. I intended to run the B programme repeatedly to see if I could spot something when it glitched. However, today it gets stuck at the M3 command. It acts like it doesn't know what to do with it. The first G0 happens, then it stops without executing the M3 at the end of the line. Hitting the Start button continues the sequence but the cutter isn't running. Trying the machine with my Rotary profile everything runs normally, so it's not the interface or other electronics. I might try to configure the Mill profile, and see if that works better.

I can't see anything in the configuration to inhibit the motor other than the output allocation, and that is the same in both, as read from the Ports and Pins menu.

One thing I notice is that looking at the diagnostics page with the Rotary profile I can get the Current Position, Machine Coord, Work Offset, G92 Offset and Tool Offset to be all zero by homing the axes (G28.1 etc) With my XYZ profile that is impossible, and I think this is something to do with the problem. I reckon it's why the Y axis hits the end stop when homing, and may be to do with the error. I had this problem before and somehow managed to set everything to zero, but I can't see how to do it again.

I've attached a picture of the two faulty Bs, and I reckon the faults are identical. This surely rules out missing steps. For measurement purposes the character height is supposed to be 7 mm, but is a bit less, and the scan is at 1200 dpi. In the runs I did I didn't see any sudden changes in all the various coordinates shown in the Diagnostics page.

One thing to note is that the fault occurs whilst simultaneously scaling the X & Y axes, and in a subroutine. From other reading it seems that either is big trouble if the offsets decide to change while they are in force, but I may have misunderstood. I can cut and paste the single letter programmes to do away with the subroutine, but not the scaling, in the hope that will help.

I am considering two other possibilities. One is to reload Mach3 but keep my profiles and screens and see if that helps. I'm also wondering about viruses. This machine is stand alone so any anti-virus on it is totally out of date. I transfer files with a USB stick from my computer, and a recent virus scan said "3 trojans found". I tried to find out what they were, what had been done with them, when they had appeared, and so on, but there is no further information. It may be that they, or something, have got into the computer and are now doing damage. I need to find a way to keep the anti-virus up to date without connecting to the internet, thus avoiding the major source of viruses!

Does any of this get us further forward?

Keith  S. Angus
Re: Skipping movements intermettently, & work offsets
« Reply #9 on: September 28, 2011, 09:34:02 PM »
Look at Config->Homing & Limits, and see what you "Home Off" position is set to.  That could explain why you can set it to 0.000 when homing.

Regards,
Ray L.
Regards,
Ray L.