On Wed, 2011-03-09 at 11:45 -0500, gene heskett wrote: > On Wednesday, March 09, 2011 11:26:57 AM Klemen Dovrtel did opine: > > > Hello everybody, > > > > Has anybody ever made a PWM triac control hal module/component or > > assemble one from existing hal modules/components? There should be one > > input signal for zero cross detector and one output signal to control > > the triac gate. > > > > If not, do you think this can this be easily done using hal? > > > > Best Regards > > Klemen > > > The two reasons I would not consider using a triac in a servo are: > > 1 the triac needs a zero crossing of several microseconds duration in order > to reliably turn off. > > 2. you are married to the powerline frequency for updating the firing angle > because once fired its going to be on for the rest of that powerline half > cycle. > > That is too slow for decent servo response. One might be able to raise the > operating frequency to 400 hz with a motor generator but at 400 hz, I'd > question the safety time to get a good shutoff at the zero crossing since > the available reset time is much shorter at 400 hz. > > This is why I'm personally in favor of a pwm driven hexfet controller, you > can, with adequate drive, turn one of them on or off in much less than a > microsecond thereby reducing the ohmic losses during the transition time, > which in turn allows it do so at 15K-50K times a second without excessive > heating, bringing real time speed control into the smaller horsepower > world. My spindle speed is so stiff I gave up and put an ammeter in so I > could see how hard it was working, it cannot be heard to slow before the > fuse clears. And this is the controller that came in my micromill, with > only the hexfet replaced because it wasn't adequately rated in the first > place. > > This style of controller can be scaled up to 10 or more kw. But it is not > a position servo, capable of holding a set position like a real servo can. >
I have 3 Fanuc servo drives (SCR) just sitting on the shelf. They are available cheap after I take off the contactor. They need ( IIRC ) 90 volts 3ph AC and 18 v dc(?). Dave ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
