Re: Going home / more stepper speed!

Hi Mariss,

I couldn't see any ringing, as my post indicated. I too had wondered if
you could detect ringing at certain step rates (filters), you could
avoid them that much easier. I did see the "sides" get rougher, but
couldn't correlate it to suspected "resonant points".

If the current at higher motor speeds does not rise to 2A, does that
indicate that my motor inductance is too high for the driver I'm using?
That the driver should use higher voltage (80v) and/or allow higher
current (3.1v)? Not needed for THAT project, although it makes a
convenient test bed at this time (motors on mill are still 4-phase). I
also saw that I probably could have used 1/2 stepping on that project.

When I go PAST the top end speed of the motor, and it stalls, I DO see a
small triangular waveform.

For now, I'm most interested in just getting clean drive out of what I
have. No plans to dynamically monitor motor currents. I will keep an
eye on that roughness on the sides of the waveform. Software generated
step pulses are another thing. If not smooth (under Windoz98), the
motor can't accelerate, and gets REAL ROUGH. Dropping into "pure DOS
mode" (or using a 622 boot disk) greatly helps that. I still have some
"distortion", I.E., some variance in the pulse rate even running at
"slew rates". So I intend to put more of the "inner loop" of the pulse
generator into assembly language, and "balance" the instruction flow a
little better.

Alan KM6VV


mariss92705@... wrote:

>
> Alan,
>
> I respectfully disagree with Jon. You cannot see ringing with either
> a voltage probe or a current probe when the motor windings are driven
> with a full bridge at low speed. This is because any back-EMF signal
> is completely washed out by the motor's inductive current and the low
> impedence voltage source that constitutes the bridge.
>
> I have tried very hard to come up with differential canceling circuit
> schemes to accomplish this because a real breakthrough would be the
> result.
>
> If it were possible to reliably retrieve this signal then it would be
> very simple to use it to use it to actively damp the ringing and also
> have direct missed step feedback.
>
> The signal is there alright, at higher speeds (>100 full steps per
> sec), it is easy to find. Unfortunately as speed approaches zero, so
> does the back EMF.
>
> Take another look at the high speed phase current with the current
> probe, but this time with the motor stalled. What you will see is a
> perfect triangle waveform. This is the motor's inductive current.
>
> If you were to subtract that waveform from the one you see when the
> motor is running (at the same speed), you would have a sinusoid that
> is pure back EMF. Most interesting, the phase relationship between it
> and the inductive current (full step drive freq) bears a direct
> relationship between pecentage of available torque (stall) and phase
> angle.
>
> >From this phase angle you can derive a feedback signal that can warn
> the PC of immenent stall in time to take corrective action.
>
> Mariss
>
> --- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
> > Jon, Mariss, Ballendo and the list,
> >
> > I did some experimenting last night, got a current probe (2ma/mv
> > Tektronix) and looked at a motor winding's current. I can see the
> > triangular current waveform of the +- 2A current responds to the
> step
> > pulses. At quite slow speeds, A pair is seen (full step). Half
> step
> > shows one current pulse with a lower amplitude. faster speeds, and
> the
> > previously separate pulses merge together, forming a continuous
> change
> > from one pulse to the next. Sometimes the "sides" of the pulses are
> > nice and "flowing" (a little wavy), other times the motor gets a
> little
> > noisy, and I see "jags" on the sides of the pulses. No "ringing"
> > observed. <snip>
>
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