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Triac and Mach3

I'm back on this one again, having made some changes and tried a few things. The problem is a lack of accuracy, after a long program the position drifts. I have replaced the computer, as it was playing up - but I'm fairly sure that wasn't influencing the problems. I have also calibrated the backlash in the leadscrews, as I found about 0.02mm of backlash in X and 0.01 in Y. Again, I don't think this is the root of the problem though -because that wouldn't be affected by the microstepping settings of the drives. I'm happy that the power supply is OK to drive the steppers (as long as speeds are kept to 800mmpm or so).

The problem isn't "odd steps" being lost, it seems far more regular than that. Running a program, then changing the microstepping settings on the drives and running the program again seems to point to a pattern of step loss. I'm wondering of the first step after a change of direction is being lost, or something similar.

The closest I've come to a solution is increasing the speed mach3 is running at and setting the drives at a very high microstepping setting. This doesn't cure the problem, but as I seem to be losing the same number of steps it makes the error smaller. Far from ideal, as it still causes problems if the program is large enough.

Any suggestions welcome, also as to a more scientific testing procedure.

Regards Kevin

Reply to
Kevin
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Kevin, Some things to try but don't try them all at once.

First thing to try is the Pulse width, go to Config, Motor Tuning and set the pulse width to 5, press save axis then OK. You only need to do it on one axis as it's common to all.

You can change whether Mach sees the leading or trailing edge by going to Config, Ports and Pins, Motor Outputs and swapping the Step low setting.

We have done about 5 Triacs now and whilst not noticing lost steps, but then again we don't run the machines for long periods before returning to their owners we have had no reports of such [ mind you I wonder if they even get used at times ? ] What I have noticed is that as you have said, the speeds have to be kept low on these 800mm / min is about average. However seeing as we fit the same electronics as we do to the Sieg machines which happily run at 1500 to 2000 mm/ min the only difference is that the Sieg's get the newer square pattern motors fitted. Non of the Denford's have had motor changes because they already have motors fitted and itis a fact that those old round 34's are far inferior to the modern square 23's.

Roy at DIY-CNC.co.uk sells some 23's rated at 3 Nm with 8mm shafts, they will run on 2.5 amp in series but ned a 5 amp drive to run in parallel.

John S.

Reply to
John S

Thanks. I had the pulse width set to 4, perhaps I should work up with it and see if it makes a difference. When I tried changing the step low setting I don't think it worked the other way round -but I'll have another check. Just to give an idea of the sort of error I'm experiencing I tried cutting a part, which should have been 26mm in x and 28.5mm in Y. It was 40mm high, cut in 0.5mm pecks -so 80 passes. At the base the size was exactly correct, but at the top it was 28.4 in Y and 25.65 in X. So the datum has drifted by 0.35mm, or 0.0043mm each pass. I'm currently set to 3200 steps per mm, so that is about

14 steps per pass. Given that movements in X on each pass are over120mm that's nearly 400,000 steps, so I realise that 14 is not a lot, which is what makes me think it's losing a step on each direction change or something. But this seems much more pronounced on the X axis compared toY, and the program was fairly equal in movements in X and Y. I'm just thinking aloud here, hoping someone might spot something I'm missing.

Regards Kevin

Reply to
Kevin

3200 steps per mm ? What step rate are you moving ?

John S.

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John S

OK, after quite a bit of testing and trials I'm still no closer to an answer -although new stepper motors are under consideration as they are the only part of the original machine not replaced. I can make the problem worse by increasing the step pulse width, and with 3 or less the machine doesn't work so 4 seems to be the optimum. I have tried reducing the acceleration to very low figures with no effect. The one thing I have noticed is that the step loss is constant in the direction. This can be changed by setting "dir low active" in the output port though. With that ticked position drifts minus in all axis, but with it not ticked position drifts plus in all axis (direction is kept the right way round be using the "reverse" setting). If I tick the "step low active" box the motors won't move. Does this make diagnosis easier, or make any sense to anyone?

Regards Kevin

Reply to
Kevin

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