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Offline Hood

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Re: controller board with encoder feedback?
« Reply #10 on: November 23, 2010, 10:08:56 AM »
You would be best to contact Dynamotion and ask whether it supports double closed loop, its not very common on even high end machine tools from what I have seen.
As for EMC I dont know, it can close the loop to the motors just like your servo drives will do if digital but whether it can then use encoders on the table as well I dont know.

There was a product that came out  that was supposed to do double closed loop but as far as I can tell it struggled with single loop never mind double.

Double closed loop is not an easy thing to accomplish especially if it is two separate parts that are trying to close one loop each.  I would imagine they would be fighting each other so in the end one of the loops would have to be set rather sloppily so as not to interfere with the other and doing that would defeat the purpose of having double closed loop in the first place.

 Just my thoughts of course, some others may view things differently ;)

Hood
Re: controller board with encoder feedback?
« Reply #11 on: November 23, 2010, 10:43:30 AM »
Thanks Hood.
So basically there isn't any controller boards that could perform the same as the Industrial cnc controller, eg. Fanuc, Siemens, etcc..
Don't know if you heard of LNC, is Linux based and I'm might consider this for my machine.
http://www.lnc.com.tw/lnc/pou/englishweb/product_520_o.htm

Offline Hood

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Re: controller board with encoder feedback?
« Reply #12 on: November 23, 2010, 11:07:18 AM »
Fanuc etc I dont think normally have double closed loop, they close the loop between the control and the motor. There may be some controls that do double closed loop but how effective it is I dont know.

If using Mach with your digital servo drives then the loop would be closed between the drive and the motor.

If your drives were analogue, in other words basically dumb drives (like a lot of industrial drives), then you could still close the loop, when using Mach,  to the motor by using the KAnalog with the KFlop or a DSPMC or Galil.

But as far as I know none of these are double closed loop, they are all single closed loop, big difference.
Hood

Offline Hood

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Re: controller board with encoder feedback?
« Reply #13 on: November 23, 2010, 11:33:35 AM »
Just had a look at the LNC you linked to and I dont see anything about that being double closed loop, in fact I would be very surprised to hear that it was.
Hood
Re: controller board with encoder feedback?
« Reply #14 on: November 24, 2010, 12:05:08 AM »
Is it possible to wire the A and B of the Linear scale to the servo driver's encoder input? since Linear scale has higher resolution, right?

Offline Hood

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Re: controller board with encoder feedback?
« Reply #15 on: November 24, 2010, 03:13:59 AM »
I am not sure what res your scales are and what res the rotary encoders on your motors are.
Often the rotary encoders are 10,000 pulses per rev so for example if motor was connected 1:1 and your ballscrews were 0.200" pitch then that would be 50,000 pulses per inch or a res of 0.00002"
 There is another thing to consider though, if considering using glass scales on an axis as feedback for motors. If you have any backlash at all in the system it would be hard to tune your motors/drives and they may be continually hunting thus actually lessening the accuracy and may even end up worse than the actual backlash.

Hood
Re: controller board with encoder feedback?
« Reply #16 on: December 01, 2010, 06:14:16 AM »
Ok, I decided not use the 2 linear scale for the moment, as I'm trying to figure out how to wire the AC servo to my BOB.
Need to solve this wiring 1st, currently I manage to make the AC servo Motor turn 1 direction using a SSR but turning the other direction is what tring to solve, anyone have any clue?

thanks
Re: controller board with encoder feedback?
« Reply #17 on: May 02, 2011, 11:24:27 PM »
Galil supports double closed loop, in fact there is an instructional video on their web site.
The PID loop must be split between the motor encoder and the scale.
Also the Kflop/kanalog cards do support differential encoders.
N.
Re: controller board with encoder feedback?
« Reply #18 on: September 10, 2011, 06:52:44 AM »
what I have done since my last reply, I purchase a used traditional Gantry Mill, travel: x 1.2m, y: 2.8m, Z: within 1 m (will check), there are 3 AC motors with chain and gears to each axis, very large BACK -LASH!.

Currently there are 3 Fagor Linear encoder + 1 DRO came with machine, will have a Mach3 controller ready for this machine.

I'm looking for a solution to reduce back lash without replacing the leadscrew to a ballscrew, what  have in mind:

1: Use a stepper card with Linear encoder input form Mbot, need a longer magnetic strip for all 3 axis.

2: DC Motor attached to each axis, then use an encoder interface to read Fagor Linear encoder's signal and feedback to the Dc Motor.

any oter ideas?

thakns