L6470 microstep positioning

[walter]

Posted on February 27, 2014 at 13:12

I mad some tests with L6470H in microstepping mode and it seems that microstep positioning is not possible with this device.

In my test a microcontroller will send a hard stop command to the motorcontroller when an external signal is detected. The controller works in 32 microstep mode, the holding current has the same value as the run current. The motorcontroller is performing a run command and wait for the hardstop command. I monitor the motor current as well as the external signal on th scope (see attached screenshots). After hardstop was received by the controller it can be seen on the scope that the motor currents are changing AFTER the hardstop and the motor keep on turning for about 10ms. #l6470

[Enrico Poli]

Posted on March 13, 2014 at 14:31

Hi,

First of all the L6470 operates in voltage mode driving, so the considerations on the output current could be misleading. About your tests: - What is the yellow signal in your waveforms? - The hard stop is always critical: the totor inertia tries to keep the motor in motion and this causes a ringing. In current mode driving the ringing is ''invisible'' from the electrical point of view, in voltage mode driving it causes a BEMF perturbation modulating the output current. - Considerations about the position must always be done measuring both the phase currents. In fact the position is the arctangent of the currents ratio. Regards Enrico

[walter]

Posted on March 14, 2014 at 08:17

Hi Enrico,

thanks for your answer. The yellow scope signal is the analog signal from a light barrier. The trigger for the hardstop is approximately in the middle of the slope. From your point of view. Are there possibilities to stop the motor at trigger point with a higher accurracy? Has the L6470 a so called break-function to shorten the motor windings at the trigger position? Regards Walter

[Enrico Poli]

Posted on March 24, 2014 at 15:26

Hi Walter,

the L6470 provides a SW input which can be used to internally generate an hardstop command when the input is forced low (limit switch). Maybe it can fit your needs (see datasheet at page 30). Kind Regards Enrico