Dave: I already have the analog output driver made and it makes a real
difference. The motor is quiet. At 2000usteps/revolution, when spinning
Shinano Kenshi SST83D1C011 motor slowly, you can see every movement clearly.
I reconnected the windings inside to be only bipolar, to get lower losses
and higher maximum RPM.
The output stage is boosted 3A amplifier, acting as a voltage to current
converter. The A/D conversion is done with a Linkwitz filter. The
preprocessing and megahertz capable quadrature inputs is done by PIC18F4431.
The firmware uses table reading in the interrupt loop. All written in
assembly. There is another function: accelerating or decelerating to
operating speed in exactly 1 revolution. The acceleration is precalculated
to be extremely smooth.
Driving stepper motors with PWM is the second worst idea in precision motors
I have seen.
EVERY TWITCH OF THE PWN PULSE GETS TRANSPORTED TO THE MECHANICS, making the
microstepping less accurate than intended!
In other words: microstepping is meaningful ONLY when you can supply
separately and precisely controlled currents to the coils, AND al low speeds
too.
But then you can separate a step into 100 microsteps, just like anybody else
on the optics industry. Steps as small as 8 nanometers are used :)
Mario.
On Fri, Feb 26, 2010 at 8:07 PM, Slavko Kocjancic <[email protected]> wrote:
> I hate step/dir as it make a lot of overhead if software stepgen is
> used. (set new direction, wait proper time, make step signal active,
> wait again, relase step signal ..... wait, .... wait)
> For that reason the best is 2 phase (quadrature) just change and forget.
>
> Let's stay on original problem/feature. Is it possible? (well the answer
> is yes but I'm not smart enought to do that)
>
>
> > Once you get much beyond 10 microsteps you are pretty much wasting
> > your time with more. There is no increase in actual mechanical
> > resolution.
> >
> > The trick is that step and direction is a "standard" and unless you
> > are making your own drivers reinventing the wheel is probably not very
> > useful.
> >
> > I remember Gray code well. I had it on some exams in college and we
> > weren't using steam engines at the time..... We were using IBM
> > punch cards to "write" software though.. ;-)
> >
> > Dave
> >
> > On 2/26/2010 11:24 AM, Mario. wrote:
> >> I had a similar idea long time ago, and I implemented it in the file,
> >> but never used. Not yet.
> >>
> >> First of all, the output encoding should use GRAY CODE format!
> >> In other words, quadrature output in 2-bit gray code. Between any two
> >> adjacent positions, there is only SINGLE bit change.
> >> Also, gray codes are used on absolute position linear and rotary
> >> encoders, which allowed useful automation back in the steam engine
> >> era ;-)
> >> The advantage of that system would be - in the era of analog
> >> microstepping - that you could change the stepper output by more than
> >> one step at a time.
> >> that would allow for high RPM of the motor, while still attaining the
> >> microstepped precision. It does consume a LOT of output pins still -
> >> but has very low latency.
> >>
> >> The theory behind that is the output code is directly translated to A
> >> and B phase currents by the motor controller from a lookup table.
> >> The disadvantage is that even for a nothing-special 32-steps per
> >> electrical period, you need already 5 pins. That is only 8x better
> >> resolution than bipolar full step (which it improves by using sine
> >> and cosine waveforms for A and B phase.)
> >>
> >> I used 32, 40, 80, 160 steps per electrical phase with great deal of
> >> success, but since the EMC2 can give output of only about 50k changes
> >> per second, that results in very slow maximum RPM.
> >> (common stepper motors have 200 steps per revolution, that is 50
> >> electrical periods per revolution, 160*50 is 8000 per revolution.)
> >> You get the idea...
> >>
> >> Mario.
> >>
> >> On Fri, Feb 26, 2010 at 7:27 AM, Slavko Kocjancic <[email protected]
> >> <mailto:[email protected]>> wrote:
> >>
> >> Hello...
> >>
> >> I'm already post that question/wish on the linuxcnc forum and I got
> >> response that here is the right place to ask that. Se here is copy.
> >>
> >>
> >>
> ;--------------------------------------------------------------------------
> >>
> >> Hello...
> >>
> >> I'm have homemade stepper driver and have phase inputs. The input to
> >> driver is 3 bit wide and is simply binary count from 0 to 7. After
> >> thinkering I modified stepgen.c and append my sequence to lokup
> >> table so
> >> modified part of stepgen.c is now like
> >> [code]
> >> /* lookup tables for stepping types 2 and higher - phase A is the
> >> LSB */
> >>
> >> static const unsigned char master_lut[][10] = {
> >> {1, 3, 2, 0, 0, 0, 0, 0, 0, 0}, /* type 2: Quadrature */
> >> {1, 2, 4, 0, 0, 0, 0, 0, 0, 0}, /* type 3: Three Wire */
> >> {1, 3, 2, 6, 4, 5, 0, 0, 0, 0}, /* type 4: Three Wire Half
> >> Step */
> >> {1, 2, 4, 8, 0, 0, 0, 0, 0, 0}, /* 5: Unipolar Full Step 1 */
> >> {3, 6, 12, 9, 0, 0, 0, 0, 0, 0}, /* 6: Unipoler Full Step 2 */
> >> {1, 7, 14, 8, 0, 0, 0, 0, 0, 0}, /* 7: Bipolar Full Step 1 */
> >> {5, 6, 10, 9, 0, 0, 0, 0, 0, 0}, /* 8: Bipoler Full Step 2 */
> >> {1, 3, 2, 6, 4, 12, 8, 9, 0, 0}, /* 9: Unipolar Half Step */
> >> {1, 5, 7, 6, 14, 10, 8, 9, 0, 0}, /* 10: Bipolar Half Step */
> >> {1, 2, 4, 8, 16, 0, 0, 0, 0, 0}, /* 11: Five Wire Unipolar */
> >> {3, 6, 12, 24, 17, 0, 0, 0, 0, 0}, /* 12: Five Wire Wave */
> >> {1, 3, 2, 6, 4, 12, 8, 24, 16, 17}, /* 13: Five Wire
> >> Uni Half */
> >> {3, 7, 6, 14, 12, 28, 24, 25, 17, 19}, /* 14: Five Wire
> >> Wave Half */
> >> {1, 2, 3, 4, 5, 6, 7, 0, 0, 0} /* 15: CAA MODE */
> >> };
> >>
> >> static const unsigned char cycle_len_lut[] =
> >> { 4, 3, 6, 4, 4, 4, 4, 8, 8, 5, 5, 10, 10, 8 };
> >>
> >> static const unsigned char num_phases_lut[] =
> >> { 2, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 3, };
> >>
> >> #define MAX_STEP_TYPE 15
> >>
> >> [/code]
> >>
> >> Now I have no clue how to update that this to be included in next
> >> relase
> >> (I don't want to recompile each relase to work with my driver)
> >>
> >> I have better idea for other's too.
> >> Maybe is possible to make step_type 15 custom. So when I startup
> >> stepgen
> >> with
> >> [code]
> >> loadrt stepgen step_type=15,15,15
> >> [/code]
> >>
> >> to use something like
> >>
> >> [code]
> >> loadrt stepgen step_type=15,15,15 step_phases=3 step_cycle_len=8
> >> step_phase_table 1,2,3,4,5,6,7,0
> >> [/code]
> >>
> >> In this way all other phase sequences can be supported.
> >> I'm just not a C programmer to do that.
> >>
> >> Is there some herro to do that?!?
> >>
> >>
> >> Thanks
> >> Slavko.
> >>
>
>
>
> ------------------------------------------------------------------------------
> Download Intel® Parallel Studio Eval
> Try the new software tools for yourself. Speed compiling, find bugs
> proactively, and fine-tune applications for parallel performance.
> See why Intel Parallel Studio got high marks during beta.
> http://p.sf.net/sfu/intel-sw-dev
> _______________________________________________
> Emc-developers mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/emc-developers
>
------------------------------------------------------------------------------
Download Intel® Parallel Studio Eval
Try the new software tools for yourself. Speed compiling, find bugs
proactively, and fine-tune applications for parallel performance.
See why Intel Parallel Studio got high marks during beta.
http://p.sf.net/sfu/intel-sw-dev
_______________________________________________
Emc-developers mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-developers
