The theory is that if the PWM signal is high the H-Bridge is switched to say
turn the motor clockwise. If the PWM signal is low
the H-Bridge is switch to turn the motor counter clockwise. Therefore with 50%
the motor is first asked to turn one way and then
the other. That results in the motor essentially being locked in place.
Change the PWM on either side of 50% and the turns in the
subsequent direction.
This is called synchronous antiphase. The advantage is there is no dead zone
around zero.
The DISadvantage is it causes a triangle-wave current in the motor which can be
quite substantial,
and causes excessive heating of the motor and power transistors.
Jon
And building these isn't as easy as it may appear at first sight. I bought a
couple of UHU boards from a company called embeddedtronics.com (no longer
around now) that didn't work. They had tried to shrink down the design too
much and encoder noised and motor noise caused unreliable motion.
Here's one of the early threads (2004) on the UHU.
https://www.cnczone.com/forums/open-source-controller-boards/14217-cnc-software-forum.html
For high power circuit layout is everything. Especially for EMI suppression.
And servo motors can generate a lot of EMI. I think that's why Gene was
talking about inductors in series etc.
Switching high currents between high/low voltage as fast as possible is
a really good noise generator. Found a layout for my cards that feels
rather good, maybe a little bit odd but should hopefully work really
well. There is common mode voltage so a common mode inductor may help.
Nicklas Karlsson
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
