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Topic: Position of a stepper motor (Read 2753 times) previous topic - next topic

lagoethe

Hello

I have a stepper motor driving a shaft with a coupling (unknown for the moment, but doesn't matter). The shaft turn of about 90°, but not exactly.

I know i can know the position of a stepper motor, but it's always open-loop.

I'd like to register the max and min position of the shaft, by moving it by hands.

Is there a way to know them with a stepper or will I have to had an encoder or any position sensor?

Have a nice day

PaulS

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will I have to had an encoder

Yes, you will have to add some type of rotary encoder. If the stepper is powered off, its just a dumb rotor. If it is powered, you should not be able to move it.

lagoethe

Thank's for the answers.

What if I supply one coil with a low  (or very low current), I'd be able to turn it with hands.

Does the sytem sees any different between coil beeing face and static to the right magnet or not and still static? or does he sees any difference only when moving BEMF (like the sensorless brushless motor)?

This is damn annoying to be able to be very precise but still beeing blind :~


PaulS

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What if I supply one coil with a low  (or very low current), I'd be able to turn it with hands.

You could, but the Arduino wouldn't know anything about you having done that.

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Does the sytem sees any different between coil beeing face and static to the right magnet or not and still static? or does he sees any difference only when moving BEMF (like the sensorless brushless motor)?

I recognize most of those words, but not in that order. Sorry.

lagoethe

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Does the sytem sees any different between coil beeing face and static to the right magnet or not and still static? or does he sees any difference only when moving BEMF (like the sensorless brushless motor)?


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I recognize most of those words, but not in that order. Sorry.


Ok sorry, I'll try again.
If you supply a coil with current, the motor will spin since the fields of the coil and the magnet are face to face. I call this position: "coil beeing face [...] to the right magnet".
Now you block the shaft of the motor. If you supply a coil with current, the motor will not spin since the fields of the coil and the magnet are face to face. I called this position:"[...] or not"
In both these cases, nothing turns, then there is no evolution of of the magnetical field, then no evolution of the current in the coil, then unuseful... this is how position is known in brushless motor, without sensors.

My question is: Even if there is no difference in coils, is there any difference anywhere that could be used.

Idea n°1 but which needed added hardware:
Rotary encoder: quite expensive If I want to be almost as precise as the stepper

Idea n°2 but which needed added hardware
Hall effect sensor: Because I don't need an absolute position but a relative one. Do any stepper motor have build-in hall effect sensors ? (need to get at least 2 to be as precise as stepper)

PS: I assumed the system was static beacause of the slow rotation speed of hand moving.

I hope this will be more understandable than previous post.

lagoethe

Ok i solved the solution, I'll use something like that: http://www.bourns.com/data/global/pdfs/3382.pdf .1 000 000 turn will be enough

Have a nice day

d00m

lagoethe

Hello !
Have you finished your project ?
whether they are useful for you ?
I wonder because I try to search the way how to know position of the stepper motor shaft..
May be this Position Encoder will be helpfull for me.
But where can I buy it ?

michinyon

You don't necessarily need a position encoder,   you need some method of determining or calibrating
the position when you power up the device.   this could be done with a limit switch somewhere.

d00m

thank you !

yes I knew about limit switch idea..
but in this variant when device is powering up, motor should move and reach limit and only after then I'll can determine its position, isn't it ?

In variant with encoder I will know position everytime I thought..

d00m

... but if we still talk about knowing position of stepper - how to do it ?
I think I really need this ability..

PaulS

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... but if we still talk about knowing position of stepper - how to do it ?
I think I really need this ability..

Then you really need an encoder that is capable of more steps per revolution than the stepper motor.

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