Correct waveform for powerSTEP01 phase current

[estie]

Posted on January 31, 2018 at 10:30

Hi,

I'm using IHMOA03 to control NEMA23 format stepper motor running in half-step current controlled clock step mode. I put the scope on the sense resistor R1 to monitor the phase current and it is not what I expected.

The motor is a six wire connection with the centre taps left unconnected: series full coil connection.

The pulse rate is circa 1kHz and vertical scale is 0.2V/div ( R1 is 0R1 ) . The wave is smoothed because R/L corresponds to about 625Hz ( 1 ohm / 1.6mH ) that's fine but I was expecting a symmetric waveform not this abrupt cut off.

Each winding should go through a cycle 0 70 100 70 0 -70 -100 -70 0 % ; ie a symmetrical cycle. Why am I not seeing this?

Slower speeds show the step nature but there is still this asymmetric switching. What is this about?

thanks.

[estie]

Posted on February 09, 2018 at 09:49

Here is a similar waveform from a slightly slower pulse rate. Here we see the PW current regulation at the programmed value ( the previous case was too fast to get to the regulated current ). Since the output H-bridge switches the sense of the current in the motor phase windings, each alternate pulse seen on the sense resistor is energising the coil with opposite polarity. That much is fine.

What seems wrong is that the half step cycle is broken and only the rising side of the cycle happens. Once at max current it cuts straight to zero.

What happened to my timed half step pulses?

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