Understanding BLDC Motor Control: Position, Speed, and Current

[bagavac]

Hi guys,

I'm developing a BLDC motor controller with load. I've bought a Maxon E40 motor . But some things i can't figure out:

I want to control position, speed and current (torque). I use PID controller to do it. In the closed loop system the output of the speed controller should be input of current PID controller.

questions:

1) is this above true?

2) is it true that the torque and current are propotional also with the load?

example: If the torque constant is 2Nm/A and my load is 1Nm i need 0,5A to move the load? or is the torque constant only propotional on no loaded motor...?

btw: why is it needful to controll the current?

 

[ayuh]

BLDC motor in printer

I am studying about BLDC motor.
My teacher gave me a BLDC motor which is in printer machine.
however I don't how to control.
It has 11 unknown outputs.(its seems to be use HALL IC 4 pins)
I have some pic about my motor but i don't how to post.
If there is anyone knowing about it.give ur opinion.
Thanks you very much.

 

[edmondng]

bldc motors are a bit complicated. there's some tutorial around the web explaining how BLDC's work. Last i work on it few months back, the current supplied controls the speed of the motor. current is controlled by chopping the driver or somewhat essentially shutting it on/off. i was using A3936.

a BLDC motor typically has 8 connector. 3 for each motor phase, 3 for hall sensor (1 sensor for each phase), 1 power supply Vcc for sensor, 1 gnd for sensor.

yes the output of the hall sensor goes back to the input. you get the timing from the motor poles through the hall sensor. from this timing, # of motor poles etc you can find the rpm of your motor. based on this result, you compare with what speed you want (ie: your speed corresponds to some timing). Increase/decrease your current to get that speed.

I got mine to work but I'm not sure if it works right. Mainly because torque is also a factor of current and speed. if you go too slow, you lose torque. So if you want to use brushless and run slow, you have to use a gear to down convert the speed.

hope this helps

 

[ayuh]

He.Thanks your opinion.
I controlled a typical BLDC motor as you say.
but the BLDC motor in printer is differ form a typical motor.
while a typical motor uses HALL sensors ,my BLDC motor uses HALL IC.
He.I can send you some info abt my BLDC motor?
Give me your email to contact!
Ok!thanks for ur help!

 

[edmondng]

what is the chip? Can you look at the data sheet for the chip. More information is required. What are your 11 pins,

 

[ayuh]

hi.i don't know how to decribe.
it will be more convient if we can contact each other by email.
are you ok?