Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: happytriger2000 on November 22, 2010, 09:46:59 AM
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Hi,
I woul'd like to know if Kflop board is the only board that support encoder feed back or there's other board that does that too?
I'm hooking up 2 Heidenhain LS 486 Linear scale to my machine, open attachment for pdf file.
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Will the Kflop actually accept the sine wave signal these scales give out? Normally you would need to use square wave output scales but as I know nothing of the Kflop it may well accept them.
Hood
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The Kflop only accepts single ended encoders, that is to say, only encoders with 2 signal wires, channels A and B. There might be a way to trick it into seeing differential signals but I have yet to figure that one out.
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hi guys,
The Heidenhain Linear scale came with a box, APE-454, please open attachment for APE-371, output is incremental TTL...
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Ok that should work.
I am not sure what you are asking in your original question as I dont know whether you are planning to use these as motor feedback or whether you are trying to use these in addition to motor encoders to get double closed loop.
Hood
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Hi Hood,
I want to build a cnc lathe, and how accurate can I get with Kflop + Heidenhan Linear scale?
What is a double close loop, and what is it for?
Freddy
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Will you be using servo motors? If yes then will these have encoders on them for motor positioning? If yes to that then I would presume you wish to add the scales to the table to give table feedback in addition to motor feedback (double closed loop). If No (motors dont have encoders) then you will be using the table scales to control motor position, this can work if everything is very tight and backlash free (not easy) If things are loose to even a small amount you may well have motor tuning issues.
So If you can explain exactly what you are attempting to use the scales to do it will help get you a better answer, ie
what type of motors(servo or stepper)
If servo do they have encoders for motor position
Hood
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Hood,
Thanks for the explanation.
Double closed loop is the answer.
My intention is to add the scales to the table to give table feedback in addition to motor feedback.
I will be using 1 x 3.5KW Mitsubishi AC servo + Driver to drive the lathe spindle, then the rest 2 axis will be using Yaskawa AC servo.
Controller board = Kflop, was going to use SmoothStepper, but not sure whether it support feedback.
2 Heidenhain Linear scale.
Cast iron lathe bed, Lathe spindle head.
will show some picture later.
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Your servo drives (if digital) will handle closing the loop to the motors but whether the Kflop can also close a second loop I dont know. I dont think it can and as far as I know no other motion controller that works with Mach can, possibly the Galil but not sure.
Hood
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what about this: http://dynomotion.com/Help/ClosedLoopStep/ClosedLoopStepper.htm
If Mach doesn't work, how about EMC2?
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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
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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
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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
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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
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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?
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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
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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
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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.
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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