UCCNC and glass scales

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UCCNC and glass scales

Postby CADdy » Mon May 04, 2020 8:24 am

Hi all,

is it possible to integrate glass scales (I hope this is the correct term) into UCCNC?

Regards
Peter
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Re: UCCNC and glass scales

Postby Robertspark » Mon May 04, 2020 8:38 am

yes they are set up as encoders

what do you intend to use them for? It is not possible to provide closed loop control

extract from the manual below, all within the documentation folder installed as default with UCCNC...
Attachments
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Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
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Re: UCCNC and glass scales

Postby CADdy » Tue May 05, 2020 5:41 am

Hi Rob,

Robertspark wrote:yes they are set up as encoders

what do you intend to use them for? It is not possible to provide closed loop control..


That was actually my intention. I know this from LinuxCNC, where glass scales are used in combination with servos for exact positioning. Are there plans to integrate this into UCCNC?

Regards
Peter
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Re: UCCNC and glass scales

Postby cncdrive » Tue May 05, 2020 7:04 am

Windows is not realtime so this is not possible.
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Re: UCCNC and glass scales

Postby Robertspark » Tue May 05, 2020 7:16 am

Uccnc will never run closed loop (as far as I am aware) because it runs on Windows and runs with a large buffer for data to the motion controller. 0.1 sec as default... My latency seems to be running at about 20mSec to 10mSec

No other windows based CNC software integrates a low latency or realtime solution..... So it's unlikely a low cost solution like uccnc will do so..... But who knows the future....

As far as I am aware (and my knowledge is limited to my own personal experience) servo drives incorporate their own position and error tracking via their own encoder inputs.... So it may be possible to swap the encoder on the end of the servo for a glass scale but it's highly likely that your servo will become VERY inaccurate.... Compared to the original solution of having the high resolution encoder on the end of the stepper motor.

Like I said my knowledge is limited to my own experience... I have 1 servo which powers my spindle on my lathe, it has a 20 bit encoder (1,048,576) .... Per revolution! Integrated into the servo motor... And it drives a 2:1 ratio htd G2 belt drive.... If this then drove a ball screw say 2.5mm pitch or 5mm pitch I fail to see how I could afford to buy a glass scale encoder which has a higher accuracy than the 20 bit one provided with the drive even with the 2:1 drive reduction.....

(My 1 servo drive is a ASDA-A2 with 750w ecma servo motor) https://www.gapp.co.uk/asda-a2

Linuxcnc is an exception.... In that it TRIES to run in real time.... Or as close as possible.... It has 2 loops one tries to run at 25uSec (40khz) and the other at 1msec (1khz)
http://linuxcnc.org/docs/html/install/latency-test.html

If you choose Mesa hardware then it runs at the slower 1khz loop with data buffered within the Mesa (motion) controller.

I say TRIES because there is always a small error which is based on what your pc hardware can do as it is being forced to run a realtime kernel.... Which is not interrupt driven as far as I am aware but uses a polling arrangement to check time elapsed (as far as I am aware which MAY be wrong!) Hence the latency (following) errors.... Close to the loop frequency but NOT bang on ..... If it used an interrupt based loop then it would be very accurate.... But it may suffer from incomplete packages of data being processed or sent (one of the consequences of using a Personal Computer to attempt to do microcontroller tasks.

Your view / others reading this may differ and I'm happy to learn something else as my experience is limited to what I have read elsewhere and my own limited dabbling with 1 servo and my limited linuxcnc dabbling with 1 Mesa 7i76e controller.
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
UC400eth, UC300eth, UCCNC v1.2110, Neuron Lite
UCCNC v1.2110 Macro Manual
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Re: UCCNC and glass scales

Postby cncdrive » Tue May 05, 2020 12:01 pm

There are realtime kernels (3rd party,not by Microsoft) for Windows though, but they are really expensive, few thousand of Euros for even single user.
With those it would be probably possible to make fully closed loop system, but I don't think that any hobby users would pay that much for it.
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Re: UCCNC and glass scales

Postby Robertspark » Tue May 05, 2020 1:07 pm

cncdrive wrote:There are realtime kernels (3rd party,not by Microsoft) for Windows though, but they are really expensive, few thousand of Euros for even single user.
With those it would be probably possible to make fully closed loop system, but I don't think that any hobby users would pay that much for it.


Interesting to know. Don't see what the benefit is though really when you can have closed loop integrated with affordable / cost effective servos.
Little point in reinventing the wheel without customers willing to buy it for a niche market.... :D
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
UC400eth, UC300eth, UCCNC v1.2110, Neuron Lite
UCCNC v1.2110 Macro Manual
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Re: UCCNC and glass scales

Postby cncdrive » Tue May 05, 2020 3:37 pm

cncdrive
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Re: UCCNC and glass scales

Postby Battwell » Wed May 06, 2020 10:57 am

what is the cost of this? anyone enquired?
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Re: UCCNC and glass scales

Postby cncdrive » Wed May 06, 2020 12:36 pm

A few thousand Euros and to make it to work in closed loop with the UCCNC we would still have to change many things in the core and do additional development, so...
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