"Peter C. Wallace" <[EMAIL PROTECTED]> wrote: > What is happening is this:
Thanks for the explanation, that helped a lot, I think I got most of it. :-) > To solve your problem there are a couple of things to try: > > 1. Live with it and offset you PDM As you say, it actually works ok with the deadband. I tuned the PID loop and I get positional errors of up to 0.067 revolutions (25 degrees), this is with no load on the motor shaft. With a 1:1 coupling from the motor shaft to a 20 tpi leadscrew that gives me +-0.004" positioning precision (not counting mechanical slop, backlash, etc). > 2. Use PWM instead of PDM (If the software PWM rate is not too low). The > ripple will be higher, but the average current in the 0 to 50% duty cycle > range will be will be higher as well. I'll give PWM a try. My pulse-generating thread runs at 20 KHz currently, does a PWM carrier frequency of 2 KHz sound reasonable? That'd give me 10 levels of power. > 3. Setup your HBridges to use 'Slow decay mode' if possible. This usually > means that the bottom 2 switch elements are turned on in the off part of the > PWM cycle, (shorting out the motor) causing the stored energy on the motor > inductance to be 'saved' between PWM cycles. This results in lower ripple, > and > more linear current versus duty cycle. I thought "both bottom switches on" was active braking. How does this help? I don't get it, but I'll give it a try too. :-) > 4. Use an HBridge with current feedback Hm, I need to read up on motor drivers... Thanks for all your advice, I appreciate it! -- Sebastian Kuzminsky ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
