Options for glass scale retrofit - component selection

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20 Jun 2022 15:57 #245487 by P1-Engineering
Currently busy getting all the hardware together to upgrade my CNC to a Mesa control with Delta A2L drives, servos and glass scales.
Unfortunatly last week I was hit by a car while cycling and as a result broke my neck. So for now I can only do all the documentation, preparation for the upgrade. 

In my preparation I'm now looking at the options for glass scales. Good info about these is hard to find, which types can be used successfully on a CNC. 
Anyone here have experience with retrofitting glass scales?. 
Due to costs I prefer to stay away from genuine Heidenhain scales. 

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20 Jun 2022 16:16 #245488 by Henk
If you are going with Mesa, any A B Z linear incremental scale will work. You can get these in TTL  5v single ended, or differential. Take the differential type if possible for better noise immunity. 

From experience, I would recommend 1um resolution, the typical DRO scales are 5um. It makes a difference, but 5um will work as well 

If you go the cheap route, I would recommend the magnetic tape type scales. These are more durable in dirty environments. I used cheap Chinese ones glass scales and they let me down everywhere I used them because of dirt ingress. Replaced with magnetic 1um scales and they are outlasting the glass ones by far
Henk
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20 Jun 2022 18:03 #245492 by tommylight

Unfortunatly last week I was hit by a car while cycling and as a result broke my neck.

Wish you a quick and painless recovery.
-
For controller, have a look at Mesa 7i95 for step/dir, or 7i97 for analog.
I suppose your drives can do both, but better make sure.
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21 Jun 2022 10:59 #245531 by P1-Engineering

If you are going with Mesa, any A B Z linear incremental scale will work. You can get these in TTL  5v single ended, or differential. Take the differential type if possible for better noise immunity. 

From experience, I would recommend 1um resolution, the typical DRO scales are 5um. It makes a difference, but 5um will work as well 

If you go the cheap route, I would recommend the magnetic tape type scales. These are more durable in dirty environments. I used cheap Chinese ones glass scales and they let me down everywhere I used them because of dirt ingress. Replaced with magnetic 1um scales and they are outlasting the glass ones by far
Henk

Ok great, good to know this is mostly universal. Btw, judging by the name, also a Dutchie?. 
I found these ones, 1um resolution and they specifically mention machine tool environments. Pricing is still reasonable I would say.

emgprecision.com/emx300-ultra-precision-...solution-gdxh-pro/#/

Or directly from the source: 
gdxhdro.com/product/digitor-readout-%e5%a4%8d%e5%88%b6/  




 

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21 Jun 2022 11:08 #245532 by P1-Engineering

Unfortunatly last week I was hit by a car while cycling and as a result broke my neck.
Wish you a quick and painless recovery.
-
For controller, have a look at Mesa 7i95 for step/dir, or 7i97 for analog.
I suppose your drives can do both, but better make sure.

Thank you, it will take some time but hopefully I will make a full recovery.

I already have a 7I76E + 7I85 (and 7I73) which I bought earlier this year when it was the last one in stock. 
Not sure if this is still the best option since the drives can also use an analog control. From what I gathered on information thus far if you plan on going full closed loop to LinuxCNC it's better to use analog control versus step/direction.

Went with these drives specifically because you can also connect your linear scale directly to the drive to close the loop. 
Currently I'm running Eding CNC, this doesn't have an option for encoder feedback. If I can't get LinuxCNC working reliably (or at all) I can still use the drives like this.
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21 Jun 2022 15:11 #245539 by tommylight

If I can't get LinuxCNC working reliably (or at all) I can still use the drives like this.

I have to say it, i have retrofitted industrial machines that are working daily for over 10 years, daily (private sector does not have free weekends here), 10-12 hours a day, never ever had any issues with LinuxCNC or Mesa boards in them.
Power outages and lightning strikes do kill the PC sometimes, but, take out the hard drive, insert it into the new PC, continue working. Literally 10 to 15 minutes of down time. In one of those factories (very close to power distribution, 2 to 3 dead PC per year) i taught the guy that works with those machines how to swap drives and always have a spare PC near. :)

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21 Jun 2022 20:21 #245553 by Henk
Haha...South African.....

Those scales will work, but check when you order, they seem to be available in different output options.

You can use step and dir interface with closed loop control. I have not done this myself but you have to set up the stepgen in velocity mode and use a pid to close the position loop.

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22 Jun 2022 23:37 #245626 by andypugh

Not sure if this is still the best option since the drives can also use an analog control. From what I gathered on information thus far if you plan on going full closed loop to LinuxCNC it's better to use analog control versus step/direction.


It doesn't really matter. There is no real difference between analogue velocity control (loop closed in LinuxCNC) and velocity stepgen (ditto). But step/dir leaves you the option of open-loop position control or closed-loop-position-control-with-pid-tweak

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23 Jun 2022 20:15 - 23 Jun 2022 20:18 #245718 by P1-Engineering

 If I can't get LinuxCNC working reliably (or at all) I can still use the drives like this.
I have to say it, i have retrofitted industrial machines that are working daily for over 10 years, daily (private sector does not have free weekends here), 10-12 hours a day, never ever had any issues with LinuxCNC or Mesa boards in them.
Power outages and lightning strikes do kill the PC sometimes, but, take out the hard drive, insert it into the new PC, continue working. Literally 10 to 15 minutes of down time. In one of those factories (very close to power distribution, 2 to 3 dead PC per year) i taught the guy that works with those machines how to swap drives and always have a spare PC near. :)
 

Not really doubting LinuxCNC's abilities, but more my own to get everything working. Got a good preview with Raspberry PI's and Klipper for the 3D-printers in terms of Linux but compared to LinuxCNC Klipper feels like plug and play to me. 
Last edit: 23 Jun 2022 20:18 by P1-Engineering.
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23 Jun 2022 20:28 #245720 by P1-Engineering

Haha...South African.....

Those scales will work, but check when you order, they seem to be available in different output options.

You can use step and dir interface with closed loop control. I have not done this myself but you have to set up the stepgen in velocity mode and use a pid to close the position loop.

Ahh, close enough. 

Thanks for heads up, will check with the Delta application note I just received regarding full closed loop. Has the full procedure on how to set it up in the drive and for instance compare it with the encoder in the servomotor.

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