unipolar motor microstepping

[mardus]

Nobody talks about microstepping by unipolar stepper drivers. Why? I'm not count on controllers with microchips (SLA ....etc...). I am interested on discrette one.
Comments ?

[kreutz]

Most of the appeal and popularity of unipolar steppers is the simplicity. You can micro-step with a discrete unipolar driver, it will just make it more complex. Just add a micro-controller, couple of D/A converters (or filtered pwm outputs from the micro-controller), sensor resistors, two comparators and a chopper circuit. Plus some programming and, voilà!, micro-stepping on unipolar!

Now, after all of this, the cost is approaching a bipolar micro-stepper driver, so, most people will upgrade to bipolar micro-stepping instead, since it offers more torque from unipolar/bipolar compatible motors.

As a learning tool the design is a good exercise.

[mardus]

Thank you for fast response kreutz.
I avoid to build bipolar driver, because I am afraid of possibility to make a smoke, due to difficulty to drive upper mosfets, as to match right dead-times and 8 mosfets instead 4 and....
I have no experience about driving steppers and I want to try something simple for the beginning.
Could you tell me something about current relations between two phase
windings in case of unipolar microstepping?

Thank's again! I hope that you understand my pure English.

[kreutz]

Don't be afraid of smoke a circuit, Do you have any idea of how many blown components and fuses took us to get a little knowledge? It does not matter how many books you read (reading is very important before doing anything, you have to have the theoretical part as clear as possible), but it is the practice what glues the knowledge into your brain. Even with today's simulation tools there is nothing like a prototype to tell you if a design is working or not.

I don't know about your electronics background, so I've got you a little tutorial (that might be a little basic), let me know. I will help you as my time allows. Don't be afraid to ask either. There is nothing difficult about electronics. Like everything in life, you have to give it a try and learn by trial and errors.

Here is the link: http://www.stepperworld.com/Tutorials/UniTutor.htm

About current relationship it is the same as bipolar micro-stepping, current in the two phases is sinusoidal (or as sinusoidal as possible, depending on how many micro-steps/step), and there is a 90 degrees phase angle relationship between them (sin/cos)

[kreutz]

Driving upper side mosfets is not a problem if you have access to the right ICs. There are half-bridge as well as full bridge mosfet driver ICs available. There are circuit configurations that won't need those IC drivers, it all depends on what voltage and currents you are aiming to.

[kreutz]

More stepper driving information

[mardus]

I just trying to find some driver ICs and Now I'm reading.... Then I'll be back.
Tnx
Tnx

[bunalmis]

Originally Posted by mardus Nobody talks about microstepping by unipolar stepper drivers. Why? I'm not count on controllers with microchips (SLA ....etc...). I am interested on discrette one. Comments ?

Unipolar microstepping driver more complicated then bipolar.

Minumum six power transistor and complex driving signals need.

Therefore not common.

(Problem is storaged energy at the leakage inductances.)

[kreutz]

Mardus;

If you are looking for IC solution to the unipolar microstepper take a look at this: http://www.allegromicro.com/sf/97060/

If you still want to build your own, using discrete components, then I can help you.

[mardus]

Bunalmis;
Where did you find six power transistors for unipolar microstepping? I never saw such design. I think that is enough four transistors (mosfets). Maybe I'm wrong, because I am new in this, but...
Yes, I suppose you mean on windings that's not in charge in some sequences. What's happening in that coils? There are some interactions between coils in charge and free coils..... Through armature....???
Kreutz;
I like to build using discrete components; it's good to learn something. With IC is easy, but I will learn almost nothing. And you know what? I am not in America or Germany or.... Here is very hard to find some special electronic components yet. Goes better, but steel ....learn with discrete buildings.

If you willing to help me and you have enough free time I'll be appreciative.

Regards
mardusster@gmail.com

[bunalmis]

Search feed forward topology. (This therm for switch mode supply)

Also this address may help to you.

http://www.freepatentsonline.com/5015937.pdf

Unipolar step motor same as push-pull transformator. All transformator has leakage inductance. If you drive it by soft signal no problem (forexample old sound amplifier) but if you want to drive with square wave signals problem begins.

One simple way you can select the four high voltage transistor and snubber circuits. Other methode is 6 transistor.

[James Newton]

Unipolar drives require only 4 drive transistors. Bipolar require 8. I'm not sure where bunalmis is getting 6, but I would be happy to be shown an example.

The Linistepper is an Unipolar, Microstepping, Open source, Current regulated Linear controller with 4 Power Transistors.
http://www.piclist.com/techref/io/st...step/index.htm

With a really nice kit of all parts, or just the PCB's available.

You haven't said how big your motors are, but if they are less than around 1.5 amps per phase and 12 volts or so, then it will work just fine for you.