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Author Topic: 1/2 speed spindle  (Read 1510 times)

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Offline Katoh

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1/2 speed spindle
« on: May 24, 2017, 04:05:43 AM »
Hi all
I just fitted up an AC servo as the spindle drive motor on a lathe, after a few exhausting days finally have something to show for the effort. All works well but has one issue that I am unable to resolve, anywhere from 0 to 1/2 its speed works like a charm but when asked to go higher the motor just will not respond, no spindle moment at all.
The lathe is controlled with a smoothstepper ESS, I have looked at the configuration and motor tuning but cannot see anything wrong.
The motor is rated 0-2500rpm anywhere from 0-1250 rpm is right on the money anything over just kills the spindle at 1260 programmed will get you 700rpm at 1270 300 and higher is 0.
In motor tuning I have the steps at 10,000 Speed at 2500 and acc at 40 Using Step/Dir as the output mode. Pulleys are et pulley1 0-2500 only one active. Smooth stepper spindle setting is at 500kHz.
If I try and use even different figures I still only end up with half that speed.
Any ideas?
Cheers
Katoh
Re: 1/2 speed spindle
« Reply #1 on: May 24, 2017, 02:46:41 PM »
Hi,
sounds like the servo drive is interpreting your pulses as CW/CCW or quadrature rather than step direction.

Craig
My wife left with my best friend...
     and I miss him!

Offline Katoh

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Re: 1/2 speed spindle
« Reply #2 on: May 25, 2017, 03:43:30 AM »
Hi Craig
I checked and double checked and couldn't find a thing, I tried doubling the speed in Mach but still when it hits that magic 1250rpm and anything over that just slows to a stop.
One interesting thing I did notice is after that when you turn the spindle off or M5 its starts and then stops. What I am saying is anything with over 1250 rpm will start the spindle,  wind it up to 1250 then stop, then its the opposite when you turn off.
Here is a pdf of the manual maybe I’m reading it wrong, not the first time.
Thanks
Cheers
Katoh
Re: 1/2 speed spindle
« Reply #3 on: May 25, 2017, 04:29:11 AM »
Hi,
do you have a scope? If so probe the pulse input to the drive and confirm th pulse rate, should be 416 kHz with 10000 count per rev and 2500rpm.

Check parameters 4, 8,9 and 10 for correct setup.
P4=0 for position control
P8=0 for step/direction
P9=1 gear ratio numerator
P10=1 gear ratio denominator

What have you set P20 to? Should be set to rated speed. For some reason P62 is also rated speed.

Let us know what you find.

Craig
My wife left with my best friend...
     and I miss him!

Offline Katoh

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Re: 1/2 speed spindle
« Reply #4 on: May 25, 2017, 08:10:09 AM »
Hi Craig
Thanks for the help!
No I don’t have a scope but I can tell you the parameters you mention are exactly what they should be, I even double checked just then.
P4=0
P8=0
P9=1
P10=1
P20=2500
P62=2500

It just seems so strange that its exactly half of the rated speed, If it was fluctuating or higher or lower than half it would lead me somewhere, but half? The only thing I think of maybe because I am only using 5V on pins 18-19 (+) side of step and direction but I can not see that as an issue as its step and direction controlled, not voltage.

Thanks
Cheers
Katoh

Offline Katoh

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Re: 1/2 speed spindle
« Reply #5 on: May 25, 2017, 08:37:49 AM »
Something I just stumbled on then, page 5 shows drive specifications and in the step and direction part has max frequency: Differential motion 500Khz and open Collector 200Khz
With motor tuning set at, steps at 10,000 and vel. 2500 gives me 416,667 steps/second = 416Hhz, If the drive is reading in open collector mode that’s double its maximum.
Problem is I don’t know enough about it to know what the difference between differential and open mode is to say that’s it, nor how to change it.
Cheers
Katoh

Offline Katoh

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Re: 1/2 speed spindle
« Reply #6 on: May 25, 2017, 09:18:21 AM »
Bugger!
I think I have found the issue, I may need to use a Differential line driver, to convert the single ended line frequency to double ended.
Instead on using 5v to pin 18-19 and the step and dir to 6-7 which apparently is open drive only giving me 200Khz input max, I need to convert this to differential (Step + and -) and (Dir + and -) which will give me 500Khz input. looking around I found these.
http://www.shop.cncdrive.com/index.php?searchstring=Differential+line+driver&x=6&y=7
Might be the answer?
Welcome to the wonderful world of servos HaHa.
Cheers
Katoh
Re: 1/2 speed spindle
« Reply #7 on: May 25, 2017, 02:24:57 PM »
Hi.
yes you'll need a differential line driver to run at full speed at max resolution but you don't really need to do you?

I mean that currently with 10000 count per rev you can drive your spindle to location 2.16 arc minutes apart.....might be appropriate
for a ballscrew on an axis but do you need it for a spindle?. If not then use the electronic gearing to reduce the resolution to something
sensible, say 15 arc min, and you'll probably run single ended OK.

P9=1
P10=10
for gear ratio 10:1, ie 1000 count rev for a pulse rate of 41.66 kHz at 2500 rpm.

Craig
My wife left with my best friend...
     and I miss him!

Offline Katoh

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Re: 1/2 speed spindle
« Reply #8 on: May 25, 2017, 07:30:01 PM »
Hi Craig
Yes I can see exactly what you are writing about, and that will work!

The only situation I see now is I also have the same motor connect to the spindle to work as a "C" rotational axis as well as a spindle. I was thinking all good when I read your post but then remembered I changed the Parameter 9 and 10 setting, where with the "C" axis you would want as much degree of accuracy as possible, But then just thinking about it now, If I use  27.7steps/deg and vel of 3600 in motor tuning for "C" axis I should in theory still have a location of 2.16min/step and a speed of 100rpm max with the parameter 10 set at 10. If that makes any sense?

Many thanks for your reply, I think you really hit the nail on the head
Cheers
Theo
Cheers
Katoh
Re: 1/2 speed spindle
« Reply #9 on: May 25, 2017, 09:18:09 PM »
Hi,
yes, I understand what you mean. The problem is that you can't change that parameter on the fly,
ie you can't use Mach to change it and then change it back after you're done unless the drive manufacturer
has allowed you to program parameters  while in service.

To be honest if your machine is accurate and rigid enuf to require C axis resolution of 2.6 arc min then you
obviously have LOTs of bucks, why piss about with Mach4? Time to get real about what you want vs what
you can achieve within your budget/expertise.

I have recently made a mill spindle with a 1.8kW servo. I will at some stage require an indexing spindle for
rigid tapping, but not 2.6 arc min!!!  15-20 arc min will be plenty good enuf for me. In the mean time
all I require is speed control, and not much of that...max spindle speed is 3500 rpm. Unless I use a large diameter
facing tool I set it to 3500 rpm and leave it there. Saves a lot of messing around to achieve little except bragging
rights. Man does this spindle make chips...glorious chips!

Craig
My wife left with my best friend...
     and I miss him!