Messages

5001

General Mach Discussion / Re: Step/Dir control of spindle?

« on: March 18, 2018, 02:07:08 AM »

Hi Roger,
I've always battled with phaselock loops, I've had some good successes but they can be very hard fought.

I made a fairly simple estimation of my servo accuracy, 20/8000=0.25%  That number comes from the Following Error window, 20 is its default.
Thus if the commanded position gets any more than 20 encoder counts away from the actual encoder position the drive faults 'Following Error'
The 'Zero Error' window is by default 4 encoder counts, thus if the error is less than 4 counts then the drive doesn't bother to try to reduce the error
further, you might say its ultimate position error is 4/8000=0.01%

Really these sorts of numbers are not truly reflective of the performance of the machine for lathe threading purposes. As you point out its ability to recover
from sudden changes in load like a tool digging into the start of a thread. My servo drive will fault if the commanded position lags by more than 0.9 degree
but whether it will fault is all about its torque reserve and the time it takes for the drive to apply the extra current. The control loop in my Allen Bradley
servo drive is 16kHz and in my own home grown one 20kHz. If I assume 10 control cycles is sufficient to have the drive increase current to match a sudden
increase in load I would expect a lag of 500-600us.

If of course the applied load exceeds the torque available from the servo it will fault no matter what happens. I can stall my Allen Bradley spindle by crashing
it into a job but it makes a hell of a bang....you may have heard it after all your only 2000nm away!

Craig

5002

Mach4 General Discussion / Re: Is there a bug with mc.mcProfileGetDouble()?

« on: March 18, 2018, 12:34:48 AM »

Hi,
I haven't encountered that however I haven't tried it either.

Certainly sounds fishy that you can delete a section and yet get a numeric, albeit 0, return.

I have on a few occasions found myself thinking that I've found a Mach4 bug only to be given an explanation as to its behavior and while that may be
quirky its not a fault.

Craig

5003

General Mach Discussion / Re: Step/Dir control of spindle?

« on: March 18, 2018, 12:23:12 AM »

Hi Roger,
when I was programming my controller for the servo I required only a PI loop. I did it using delays, I guess you'd say a Z plane approach, very similar
to the s plane approach. I found that how you managed integrator wind-up rather more important or at least as important than the PI gain constants.

Craig

5004

Mach4 General Discussion / Re: Is there a bug with mc.mcProfileGetDouble()?

« on: March 18, 2018, 12:10:58 AM »

Hi,
haven't tried it so can't really help, although I have a question.

Is 0 not a value? The way I read it is that if the value does not exist ie null then it would return your default.

Craig

5005

General Mach Discussion / Re: Step/Dir control of spindle?

« on: March 18, 2018, 12:03:15 AM »

Hi Roger,
yes those Baldor servos are the very best quality, you certainly want to keep using it, whats the bet it outlasts us both.

Is it fitted with an encoder or a resolver? I know a lot were fitted with resolvers. I have a big kick-arse servo  fitted with a resolver and I'm making a Field Oriented
Control for it. The TI micro does a very nice job of producing sinusoidal excitation and synchronous detection. It could be done analogue, in fact I did make an
analogue exciter while I was experimenting but it becomes very time consuming. In fact, except for very simple stuff, high quality analogue is more time consuming
than digital.

If I were designing/making something that might find some modest market appeal I would go digital because of the flexibility it confers. Rather than change a resistor
or capacitor for adjustment of a PID loop for instance a simple parameter change with a digital solution. If I were making for myself I would be more inclined to an
analogue solution, I still get a blast out of designing my own analogue circuits. Under those circumstances I would be doing it as a hobby and any time I spend is
for fun.

How close or tight do you want the control to be? I would guess that a load/no-load regulation of a few percent would suffice for lathe threading...would you agree?
Either digital or analogue would achieve that easily. Beyond that level of control analogue becomes increasingly difficult, any drift or leakage current or noise.....
and control accuracy goes out the window.

My AC servo, within its torque limit (rated 6Nm, O'Load 18Nm) is good to (20/8000)=0.0025 or 0.25%. You can see why I like these AC servos ....1/4%... straight out
of the box!

Craig

5006

General Mach Discussion / Re: Step/Dir control of spindle?

« on: March 17, 2018, 09:03:37 PM »

Hi Roger,
sorry about my rant, as you can tell I'm enthusiastic about AC servos, you might say I've had my eyes opened.

Basically, it would just need to be a phase-lock loop with an analog output. The Index pulse would still go through to Mach3 for threading sync, but the spindle speed would now be rock-solid.

I think that would work. Essentially the step pulse from an ESS is proportional to required speed as reflected by the encoder. If you feed the step pulse and the
encoder feedback into a frequency discrimination circuit you would end up with an error term which could be applied to your drive.

I personally would approach the problem slightly differently. I would have the step/dir pulses cause an accumulator count up/down to reflect position.
An identical accumulator would count up/down with encoder position and the difference between the two accumulators would be the required error term.
Obviously I am anticipating doing this on a micro. As a result of another project I bought a development board of Texas Instruments with a TMS320F28069
32 bit microcontroller with on board everything, single cycle 32 bit floating point.....and the list goes on. $47NZD +15%GST free shipping. It might be like
using a sledgehammer to crack an egg but POWER to burn!

Given my new found enthusiasm for AC servos and the realization that servo manufacturers are very VERY good at getting the best from their products
all the effort involved in making my own feedback loop would be undertaken for interests sake/bragging rights only.

Craig

5007

General Mach Discussion / Re: Step/Dir control of spindle?

« on: March 17, 2018, 08:37:08 PM »

Hi Roger,
a modern AC servo leaves the ESS PID solution in the dust.

Of course you know that at this time it is limited to one pulse per rev. Andy has expressed interest in extending that to multiple pulses per rev. As you also probably
know many ENTRY level servos are shipping with 17 bit encoders, A Delta servo I've been giving a hand with in the forum has a potential encoder count of
160,000 per rev. Will Andy be able to squeeze that in?

My servo is about 10 years old, Allen Bradley and is equipped with a 8000 count per rev encoder.....very ho hum by todays standards but has proven to really REALLY
spin my wheels! I had to buy the software to program the EMPROM, I would have had it gratis had I bought new, but this is second hand.

Anyway the software has a database of all Allen Bradley servos, mine included and many of the basic parameters are set just by virtue of selecting your servo from
the list. The basic parameters include such things as rated speed, rated current, encoder count etc, all the usual stuff. What may not be apparent is the detail about each
servo, the resistance and inductance of the windings, a table of flux density verses current....yes that's a quasi linear approximation of hysteresis, thermal mass and
temperature rise. In short the database has more information that you could expect to find or measure yourself.

There is the opportunity to adjust the PID parameters if you wish however the database entries have proven to be better than me fiddling with them for hours.
Amongst the facilities of the software is an Oscilloscope where you can plot loop error verses time, just brill....I can see at a glance the damping factor a damn near
0.7071, just what I'd try to achieve if I were fiddling with it...and to have it displayed as a live oscilloscope trace!

In short modern AC servos and their drives with the software support from the manufacturer make old school PID loops look like crap. I bought my servo and drive
including shipping for $800 NZD or about $600 USD. Quite frankly for that sort of money why would you bother with a DC servo?

Craig

5008

General Mach Discussion / Re: STEPCRAFT 840 to Mach3... Help

« on: March 17, 2018, 08:07:52 PM »

Hi,
according to the advertising material this machine is supplied with UCCNC software and a UC100 motion controller.

Do you in fact have either or both?

Craig

5009

General Mach Discussion / Re: Step/Dir control of spindle?

« on: March 17, 2018, 07:36:53 PM »

Hi Roger,
Mach4Hobby allows one out-of-band axis and it is always a spindle. As the attached pic shows it can be driven step/direction.

Given it is an out-of-band axis it is not constrained to motion end points like coordinated axes.

Hobby allows for one OB axis whereas Industrial allows six. At this stage I can't find a means of having Hobby drive my spindle as an indexing axis.
That is to say that the API doesn't apparently allow position commands only speed commands. Exactly how rigid tapping works I don't know.

I can make my spindle index by switching its pulse inputs to the A Axis. Of course the A axis is coordinated but if all I require is an indexed move
I can do so in one move provided there are no other axis moves on the same Gcode line. There might be some overlap due to  CV at the end of the index move.

I consider it a shame that NFS have limited Hobby to one OB axis and also that it has only speed control. I'd love to be able to play with Industrial to see
how those extra OB axes are handled.

Craig

5010

General Mach Discussion / Re: Servio motor Delta adas b2 Software and electronic gear ratio

« on: March 17, 2018, 06:11:23 PM »

Hi,
please post a screen shot of your motor tuning page.

Craig