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Author Topic: Spindle/ C Axis using CSMIO/IP-A  (Read 2083 times)

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Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #10 on: October 13, 2018, 05:10:43 PM »
Hood

I have read the reply from CS Labs a few times and I am wondering if the second line is hinting at it being possible to do something like SwapAxis() feature in Mach except via VB scripts. It might be worth asking them to clarify.

I will ask for further clarification on Monday. Can you please clarify exactly what is meant by indexing? I thought this referred to set index points EG (1 degree, 10 degrees, 20 degrees etc) which is not a fully functioning rotary axis. With an accuracy of 0.1 degrees as stated by CS Labs, would this not be useless for any kind of semi-precision work?

 If you were machining a part with a 150mm diameter that would give you an accuracy of 0.13mm (150x3.142/360x0.1)  

I like the magnetic clutch idea will do some research on those. Don't think Mazak will steal my idea in a rush. lol :-[

Bill

Thanks for your comment.

Looking at the moment to keep the original spindle and VFD and using a small Servo motor geared down for C axis machining.  

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Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #11 on: October 13, 2018, 05:22:02 PM »
Are you planning on using it as a rotary axis? I was thinking it was just indexing you were wanting, if not then that is a different.
Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #12 on: October 13, 2018, 05:50:43 PM »
Hi Mick,
if I understand you are using the original VDF/spindle motor currently? How does it perform?
Induction motors and VFDs are a poor choice for indexing/C axis work but for normal turning operations
are more than adequate.

As you know I have a servo for a slow speed/high torque spindle. My initial use of it was in velocity mode and I would present
the servo drive with a +10/-10 V signal.....easy.

More recently I have been experimenting with the same servo but in Step/Direction mode and using it as a continuous
running spindle. Mach4 has a quite extensive suite of APIs that make this possible.

My most recent experiments have revolved around having the 'normal' spindle defined (Step/Dir) AND an Out-of-Band axis.
In Mach4 you can have up to six Out-of-Band axes which can be jogged. Thus I have two Step/Dir input pairs available for my
servo spindle. I select one pair as required for the machining operation at hand.

The trick is that when the spindle is in free running mode that it will lose reference. Thus when I finishing the free running operation and wish to
index my spindle I have to home it and then I am able to jog to a given angular position. What I am working on is having Mach keep track
of the encoder during free running mode so that it does not lose reference.

My most recent experiments have gone a step further. I have the same normal free running spindle, I have an indexable (via jogging) Out-of-Band spindle
and have a genuine C Axis which has coordinated motion with the other axes for things like rigid tapping. Thus I have three separate modes of operation
programmatically selectable.

All in all it has absorbed a great deal of time and programming effort. Given that 99% of my milling requires just a free running spindle the question must
be asked 'does all the complication of an indexable and/or C axis make sense?'. Probably not... however it has kept me off the streets and I have learnt
a lot about Mach4 and programming it. If what is learnt in pursuit of your hobby is considered valuable, then this has been worthwhile.

Craig
My wife left with my best friend...
     and I miss him!
Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #13 on: October 14, 2018, 09:08:31 AM »
Hood

The plan is to use it as a rotary axis at some point. 

Craig

 Induction motors and VFDs are a poor choice for indexing


The Jaguar 550 VFD works fine with the original motor and it was never my intention to use it for any kind of indexing or rotary axis. Only for turning and threading. Hence why we are talking about fitting a 1.5kw servo motor alongside the original spindle motor. 

Given that 99% of my milling requires just a free running spindle the question must
be asked 'does all the complication of an indexable and/or C axis make sense?'. Probably not...


This is something I would like to do and I don't believe it would be that difficult setting this up as a separate axis. 

Mick

 

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Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #14 on: October 15, 2018, 03:27:26 AM »
Thinking about it, with two clutches, spindle and C set up on their own channels then it should actually be possible to use one profile and both for the same part.
Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #15 on: October 15, 2018, 07:58:53 AM »
Hi Hood

I think I may be missing something here but if I use the existing VFD and Spindle motor why would we need to use separate profiles? The spindle is using the 0 to 10v analog output from pin 7 or 8 on the I/O connector and the encoder will be connected to the csmio/enc. The C axis will be treated as its own axis not a spindle the same as X and Z and use one of the encoder channels on the I/O. The analog voltage to the C axis will come from pins 1-6.   
Does this sound right? Are we talking about the same thing? 

These clutches look great. Not going to be a standard fitment though and I think expensive. Do you have any supplier contacts?

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Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #16 on: October 15, 2018, 05:22:13 PM »
Ah, yes that would probably be correct, kind of muddled up here as you started off with one servo for both spindle and C but have now moved on to two separate motors/controllers (VFD/Induction and Servo/Servo drive)

You would still need to disengage the  Servo as any motion on it would be detected by the CSMIO and it would try to correct and would throw a fault although probably not when disabled but not sure how easy that would be to do, if at all, from within Mach/CSMIO. Even if a way can be found then I don't think driving a servo motor would be the best idea for a drive even with it disabled.

Don't really have a source although I do get them every now and then, in fact just threw one out a few weeks ago, it was on a Jabso pump that came from a boat I did a refit on, it kicked about my workshop for months  and was getting in my way. Nobody wanted it due to it being 12v and most boats are 24v so in the skip it went.
Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #17 on: October 16, 2018, 04:49:59 AM »
Hi Hood

You would still need to disengage the  Servo as any motion on it would be detected by the CSMIO and it would try to correct and would throw a fault although probably not when disabled but not sure how easy that would be to do, if at all, from within Mach/CSMIO. Even if a way can be found then I don't think driving a servo motor would be the best idea for a drive even with it disabled

Totally agree some kind of clutch is needed to disengage the servo.

My main concern at the moment is the accuracy of the C axis. The manual for the Lexium 28 drives states an accuracy of 0.044 of a degree. The resolution of the encoder is factory set at 2048. So I think this is 2048 x 4 =8192PPR. So 360 degrees/8192= 0.044 degrees. If I take a 150mm max turning diameter this would give me an accuracy of 150 x 3.142 = 471mm. So 471/360= 1.31mm per degree. 1.31x0.044=0.057mm. (Think that's right) :-\
Ideally, I would like to have an accuracy of around  0.01mm.

I would need to either gear the servo motor 5/1 or change the encoder resolution to achieve this. I do need to gear the servo motor at least 2/1 for torque purposes and hoping I can adjust the encoder resolution to do the rest?

This encoder resolution can be adjusted via P1-46 up to a value of 40,000. I have tried adjusting this on the X and Z axes but got some strange results.

I'm trying to figure out why Schneider would state an accuracy of 0.044 when the parameter allows you to set a lot finer resolution possibly which would give you more accuracy. 
Have you adjusted the encoder resolution on any of your drives?

Attached a couple of manual screenshots.

Mick
Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #18 on: October 16, 2018, 11:41:13 AM »
Looking at the electromagnetic clutches and this type of thing is available off ebay.

 https://www.ebay.co.uk/itm/Genuine-John-Deere-Electromagnetic-PTO-Clutch-AM119536/183059126213?epid=1516104299&hash=item2a9f2c97c5:g:9M0AAOSwyphaedn8:rk:7:pf:0

Can't get any holding torque data but spoke to a few suppliers and they are fitted to lawnmowers with an engine size of 12hp plus. Would have to make a reducing coupler from 46mm down to 1" and change the pulley to HTD type. Any thoughts whether something like this would suitable?

Also thinking would this have to be fitted on the spindle side due to possible magnetic interference to the servo motor encoder?

Mick
Re: Spindle/ C Axis using CSMIO/IP-A
« Reply #19 on: October 16, 2018, 02:17:41 PM »
Hi Mick,
the encoder resolution of 2048 lines/rev is the simulated encoder.

The servo encoder and the servo drive have much finer resolution that that. I think the servo encoder is 17 absolute and therefor has a potential
resolution of 170,000 counts per rev.

You could theoretically increase the simulated encoder resolution up to the same 17 bit. Given that the CSMIO closes the loop then the simulated encoder
resolution is the limiting figure. The downside is that the CSMIO has limited signaling speed, and in any event signaling over 500kHz between controller
and servo drive is DIFFICULT at best there is therefore a practical limit to the resolution beyond which the signaling speed limits the rotational speed.

The second issue is the 'zero error window' My servo has a programmable window, 4 encoder counts (out of 8000) by default where the servo drive
determines that the actual position is close enough to the commanded position that it will not try to close the error any further.  You can reduce the
zero error window however the servo will 'hunt' when its close to its commanded position, sometimes you will hear it as a buzz. I use the servo drive
to close the loop and therefore use the servo drives manufacturers programming facility to do this. In your case you will have to use the 'zero error
window' feature or its equivalent, if it has it, in the CSMIO.

My experience is that for practical purposes that a resolution of 0.18 degrees or 10.8 arc minutes is realistic even if greater resolutions are theoretically
possible. Thereafter gear reduction is the only feasible way forward. Consider a harmonic drive.

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