Bipolar Stepper motor

[MAKInnovation]

I have derived a bi-polar stepper motor with full step and half step techniques successfully.
It is an easy part of driving a stepper motor but the difficult one is to determine the position of stepper motor.
....... so i really need to know that How it can be done?

[Ttelmah]

Normally, stepper motors are controlled as 'open loop' devices. You design the hardware, so the motor is not overloaded, then send your train of movement pulses to it, and 'count steps'. You know the count, so you know where the motor 'should be'. You can even store the count when power is removed to 'simulate' a system that knows it's position.
To make a stepper fully 'closed loop', would involve adding something like an optical shaft encoder, and reading the position using this. However this is a rare approach, since once you add the complexity of an encoder, you are well past halfway to the extra costs of building a servo instead, and with this, something like a BDLC motor can be used instead of the stepper to give higher performance.
One slightly more common approach is to have limit switches on a stepper based design, so you know where 'home' is, and can reset the counter at this point, to give a better starting point.
So, normally you just count pulses.


Best Wishes

[SherpaDoug]

For example a desktop ink jet printer usually uses steppers to position the print head and paper.

Every time a new sheet of paper arrives, a switch senses the edge of the paper. The printer counts stepper pulses from that edge.

When you turn on the printer the print head always goes to one side where it hits a switch to let the printer know it is home. The printer counts stepper pulses from there.
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The search for better is endless. Instead simply find very good and get the job done.

[MAKInnovation]

But my case is bit difficult.
here stepper is used as valve to open and close the gas pipe.
I can not find when shaft attached to stepper hit to either end.
I am unable to stop the pulse train even the shaft is at home position only because I don't know about the position of shaft attached to stepper.

*Either End = home position(completely open) Or extreme position (Completely closed)

[temtronic]

You could monitor the gas on either side of the valve. Simpe logic, if both pressures are equal valve is closed...
You could monitor the 'stall curent' of the motor. Again simple logic, if stall current exceeds a preset, known amount, you've stalled the motor. Ie, it's trying to go past one end or the other. What direction you're going is already known, hence fully open or closed.
Simplest of course has already been offered. Two micro limit switches.

[MAKInnovation]

I checked with the voltage and waveform.
It can not be possible to figure it out with the voltage variation at middle or at the ends. I have already checked with it.
I observed the very very slight change in waveform shape. Which obviously can not distinguished with any logic.

I will check with the stall current method tomorrow in my office and then post my working.

[Ttelmah]

Really I have to say, 'why use a stepper'. Seems to be the wrong tool for the job. Just use a simple geared DC motor, and when the current rises you have reached the limits....
Faster, smaller, simpler.

Best Wishes

[FvM]

[MAKInnovation]

[gpsmikey]

The limit switch is the best idea (or an optical isolator or even a hall effect sensor with a magnet - it depends if the valve control is multi-turn or if it is more of the 1/4 turn type. The 1/4 turn type would be the easiest to work with using at least 1 limit switch (or limit detector of some sort). If it is a multi-turn valve type, it is going to be a bit more difficult.

mikey
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mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

[MAKInnovation]

It is a multi turn valve. & take many steps to reach to either side.
I am actually curious if there is any idea for position detection without tampering with hardware.

[gpsmikey]

For a multi-turn valve and not modifying the existing hardware, either the load current idea or my preference would be an optical interrupter on the shaft of the stepper motor to allow you to detect motion. When you step and it does not advance, you are either at a limit or it is stuck. Not sure just how you determine the difference on that (stuck vs limit). The optical interrupter on the shaft would give you feedback though so you could tell if the motor was actually turning.

mikey
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

[MAKInnovation]

how can we install optical interrupter with the shaft and how it will work.
Confused and need some more detail.

[Ttelmah]

[FvM]