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Author Topic: Quastion about 2 motors on one ax and correcting by encoders  (Read 6944 times)

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Offline Inna

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Quastion about 2 motors on one ax and correcting by encoders
« on: November 06, 2008, 05:04:25 AM »
Hello everybody!
Please help to new user. I was searched an analogical theme, but did not find it. Give me please link, if this theme understood already.

Problem: I have tow motors on one ax. I try to use X ax stepper motor as master and A ax stepper as slave for synchronous mowing. Both motors have encoders(but not connected yet).
I was turn on A as slave, turn on "Formulas", where f(a)=X or f(a)=x*(-1) and in the "General config"->"Home slave with master axis". And nothing changed - A ax don't move, when I press arrow keys, or MDI.
Both axis move just when I press "GOTO Z".
Who know what I do wrong - please help.

And one more. Does anybody know how to turn on motor correction by encoder. I was connected encoders and in the settings screen I see that its work, but it have no affect to motors. Explain please, how it must to work.

Thanks. Inna. 

Offline Hood

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #1 on: November 06, 2008, 07:28:42 AM »
Encoders with mach can only monitor, Mach is Open Loop control.
Cofig menu then down to Slave Axis then enter which axis is slaved with X Y or Z.
Hood

Offline ger21

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #2 on: November 06, 2008, 09:02:53 AM »
Get rid of the formulas, you don't need them to slave.
Gerry

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #3 on: November 06, 2008, 10:31:38 AM »
I never understood this. If mach can monitor the encoders why can't it also correct the position. Is it a timing issue of using a PC?

Offline ger21

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #4 on: November 06, 2008, 01:33:46 PM »
It doesn't "monitor" the encoders. It just reads the data from them and displays it (if you add the correct DRO's). Mach doesn't have time to do anything with the data. And when you talk about correcting position, you open up a whole new can of worms. Such as, how do you correct the position of a stalled stepper, since it can't move, because it's stalled? :)
Gerry

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http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline Inna

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #5 on: November 06, 2008, 02:38:50 PM »
Thanks guys!
Second motor started, after reinstall Windows. But at the A DRO it does not show!
Its so sorry, that Mach cant to correct motor position by encoder.
What do you think - if use the Brain, for this? For example something like this:
EncoderX+-0.01mm<>XDRO ->Terminate E-Stop. I'm not sure that possible to do that without VB, but...
What do you think?
Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #6 on: November 07, 2008, 11:13:13 AM »
I never understood this. If mach can monitor the encoders why can't it also correct the position. Is it a timing issue of using a PC?

Mach CANNOT monitor the encoders. 
It runs only open loop.
It can only give a position command to the drives.
The encoders are ONLY monitored by the servo drives (or stepper drives) to get the motor to the proper position.

Scott

« Last Edit: November 07, 2008, 11:14:52 AM by polaraligned »

Offline Inna

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #7 on: November 07, 2008, 04:17:27 PM »
Ok! Lets continue theme if nobody against?
Maybe anybody know how to resolve this problem?
I have an idea:
For example take Atmega16. Steps and dirs impulses for both motors send through Atmega and feedback from encoders too.
Start timers and counters and compare impulses in an interval between a start and completion of timer.
If a difference appears between impulses from first and from second encoders, Mach must stop motors. Or to put on the brakes the first motor, while the amount of impulses will not be evened.

What do you think about it? 

Offline Hood

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #8 on: November 07, 2008, 06:39:38 PM »
Inna, I am not sure if its possible but seems to me you could  connect the  encoders to inputs in Mach and have a Brain look at them and compare to the axis DROs. If the difference is greater than a certain amount then call an E-Stop. One thing you would have to do is sync the Encoder DROs with the Axis DROs after the machine has homed and the Brain I would think would need to be active only when homing and syncing is completed.
Hood

Edit
 Ron Rogers sells a board that does this so might be the best option   www.rogersmachine.net
« Last Edit: November 07, 2008, 06:42:49 PM by Hood »

Offline Inna

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Re: Quastion about 2 motors on one ax and correcting by encoders
« Reply #9 on: November 08, 2008, 10:29:18 AM »
Thanks Hood!

I think exist other way! To use servomotors! Maybe anybody know lowcost servomotors and servodrivers which can Mach use?