L6470 Stall detect issue

msmith · ‎2014-07-24

Posted on July 24, 2014 at 15:26

Hello, I am posting this question that another user posted but there was no answer.

Can anyone help?

Can't reliably sense stalling using L6470 chip

I've been quite successful at controlling the L6470 stepper driver chip from my embedded ARM processor for all features other than the sensorless stall detection feature. I'm hoping that I'm missing something and that someone can point that out to me. I've been all over this forum and every scrap of ST documentation I can get my eyes on.

When I try to detect stalling, the detection threshold seems to be very sensitive; at one current setting the chip never detect any stalls, and at the next increment of stall threshold current the chip always shows stalling. This pretty much makes the feature unusable, so I'm not using it. I would really like to be able to use this feature, since we can't afford to put encoders everywhere. Also, it's one reason we picked the driver chip, so it will be disappointing if we can't use that feature.

Am I missing something obvious? Is there more documentation around this feature other than what is contained in the L6470 datasheet?

Thanks, Mark

#stall-detection-l6470

Enrico Poli · ‎2014-08-21

Posted on August 21, 2014 at 14:25

Dear Mark,

the sensorless stall detection effectiveness depend on the BEMF of the motor, and in particular the current variation it causes between the run (BEMF is present) and stall condition (null BEMF).

Can you check what is the current variation in your case?

A limited current variation can be due by the following conditions:

- low speed operation (low BEMF is almost equal to no BEMF)

- high speed operation (inductive drop is dominant compared to BEMF)

- stepper motor with low ke value

Regards

Enrico