Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Inna on November 06, 2008, 05:04:25 AM
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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.
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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
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Get rid of the formulas, you don't need them to slave.
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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?
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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? :)
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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?
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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
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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?
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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
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Thanks Hood!
I think exist other way! To use servomotors! Maybe anybody know lowcost servomotors and servodrivers which can Mach use?
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This might sound stupid - but why can't you run both motors from the same driver - given that the drivers can output sufficient current. It is only like me wiring my eight wire motors in series or parrallel.
In that way, both motors get exactly the same pulses.
If one of the motors is consistently missing steps, that is a mechanical problem - not an electronic one, and should be treated as such, Don't try and impose an electronic answer on a mechanical problem.
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This might sound stupid - but why can't you run both motors from the same driver .........
Mariss from Gecko has said that you can. BUT. only up to about 200-300rpm. Above that you run into problems, but I don't recall exactly why.
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:)
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Friend!
Please advise the servomotors, which can good work with the Mach, and have step and dir pins.
Thanks!
Inna
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It is the servo drive that needs to accept Step/Dir rather than the motor, there are many drives that do that but you will have to be more specific about your needs before anyone can advise what you need. As an example I need large servos for my machine and I have used Allen Bradley and Giddings and Lewis AC servos and drives. If you dont require such large motors then you can look at the Geckos, Rutex, Granite Devices, Tek10's, Vipers etc.
Hood
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Thank you Hood!
Company which I work in, makes cnc-machine recently, and we yet pick up the best variants for our machines. (I mean inexpensive and reliable decisions).
We used for it different steppers, one time for plasma CNC we used Lense gear-servomotors, it is work good, but this is expansive way. I search good alternative, cost like steppers and reliable like Lense. :)
Usual we need shaft speed ~ 300-600 rpm, still torque ~12N/m, and motor weight - than less, than better.
Thanks.
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Afraid to say Cheap servos and 12Nm continuous torque are not words that you can put together. That is industrial servo territory and that is why I have Industrial servos/drives because I need that class of motor.
Some of the Chinese guys are bringing out motors and drives of that size but how good/bad they are I have no idea.
Hood
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I was not correctly expressed possibly! When I talked price as Steppers, I exaggerated. Such effort needs us on the billow of reducing gear.
My director ordered to me, to choose servomotors, purchase a few motors and drivers which I'll advise, on ebay, for an experiment. As I understood, after good result, he plans to buy already at the distributors.
Thanks.
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very nice servo motors http://www.ms-motor.com/acservo.htm
and some prices of them- made in China.
---AC SERVO MOTOR
-57 Series Low Inertia AC Servo Motor
30W,price is 440USD/SET,include motor ,driver,cables
50W,price is 440USD/SET,include motor ,driver,cables
100W ,price is 440USD/SET,include motor ,driver,cables
-60 Series Low Inertia AC Servo Motor
200W,,price is 430USD/SET,include motor ,driver,cables
400W,,price is 440USD/SET,include motor ,driver,cables
600W,price is 510USD/SET,include motor ,driver,cables
-80 Series Low Inertia AC Servo Motor
500W,,price is 550USD/SET,include motor ,driver,cables
750W,,price is 560USD/SET,include motor ,driver,cables
1000W,price is 600USD/SET,include motor ,driver,cables
-92 Series Low Inertia AC Servo Motor
500W,,price is 530USD/SET,include motor ,driver,cables
750W,,price is 560USD/SET,include motor ,driver,cables
1000W,,price is 620USD/SET,include motor ,driver,cables
1200W,price is 640USD/SET,include motor ,driver,cables
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ms-motor.com is not good as https://www.oyostepper.com (https://www.oyostepper.com/).
I have diy 2 cnc projcets, all my nema 17 stepper motor (https://www.oyostepper.com/category-6-b0-Nema-17-Stepper-Motor.html) from this site.