L6470 loosing steps

stefan2399 · ‎2013-07-16

Posted on July 16, 2013 at 16:10

Hello,

I am evaluating the L6470 as replacement for a discontinued chip, which is used in our application in the moment.

I have to reach high speed (2500 step/s), however when going above 800 step/s the motor looses steps. Here are my motor characteristics: according to datasheet:

Rm = 0,8 Ohm

Lm = 1 mH

(I measured Rm = 3,3 Ohm; Lm = 5,3 mH)

ke = 0,115 V/Hz

I use 24V power supply.

I tried a lot of different parameters with dSPIN Evaluation tool, but 800 step/s seems to be the upper limit, although the old motor driver reaches 2500 step/s easily.

Does anyone have a hint for me?

BTW, I'm evaluating with EVAL6470H board.

regards,

Stefan

Enrico Poli · ‎2013-07-18

Posted on July 18, 2013 at 16:38

Hello Stefan,

the issue is probably related to the mid-speed resonance of the motor. If the motor is unloaded I suggest you to add a small load on the shaft (e.g. adding few rounds of adhesive tape), this way the resonance should be dampen a bit and the step-loss is avoided.

BR

Enrico

stefan2399 · ‎2013-07-22

Posted on July 22, 2013 at 15:36

Hi, Enrico,

thanks for your fast reply. I tried both, with and without load, but there is no difference. I took a look at the oscilloscope and found that the current peak is not in the center of the step (see attached file) Is that normal? If not, which parameter changes this behavior?

________________

Attachments :

scope_1.bmp : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HzDh&d=%2Fa%2F0X0000000bJL%2Fxj7tiOh.lIL.ccAOyKLDVjWxpj51l_ntK1U6Rg7j1VI&asPdf=false

Enrico Poli · ‎2013-08-01

Posted on August 01, 2013 at 10:44

Hi Stefan,

The phase relation between the output voltage and the motor current depends on the electrical characteristics of the motor and the mechanical load, so the waveforms are ok.

Did you try to increase the motor current? Maybe it is not enough to keep the motor running at that speed.

Regards

Enrico