On 1/5/2010 12:15 PM, Sebastian Kuzminsky wrote: > Dave wrote: > >> On 1/5/2010 11:49 AM, Flying Electron wrote: >> >>> >>> Since you have a mesa card, maybe you or anyone else that has a mesa >>> card can explain how the servo PID works with the mesa in EMC. Does EMC >>> do the PID calculations and just send a command to the mesa board or >>> does the mesa board do the PID calculations and just tell EMC where the >>> servo currently is? I guess another way to rephrase that is, is the >>> mesa board closing the loop or does it need EMC to close the loop? >>> >> As far as I know, all EMC2 servo solutions solve the motion PIDs within >> the PC, not on any cards. >> > EMC2 can run either way - closing the servo loop on PC inside emc2, or > letting the servo controller do it. > > Mesa cards (and other similar hardware) expose the servo encoder to > emc2; emc2 does the PID calculation and computes a signed-magnitude > motor control value; this gets fed to the motor amps. This is nice > because you get full insight into what the motor is doing, and you can > easily tune the PID controller. I dont know for sure, but I suspect > that emc2's PID controller is better than most embedded solutions; it > has first- and second-order feedforward etc. > > Gecko servo controllers (and other similar hardware) consume the servo > encoder information; do their own PID calculation; and feed the motor > the proper power. In this case, emc2 communicates only "desired > position" information to the controller, usually via step/dir signals. > This is nice because it makes it very simple to get the motor up and > running. > > > Whoops... sorry.. that was silly. I wasn't thinking about step and direction, but that is a good way to get position info to a drive/controller so it can close the servo loop. Step and direction works very well tied into drive controllers like or similar the Automation Direct servo drive systems. Those are self tuning as well which makes setup really easy. They aren't cheap but industrial grade servo stuff is not cheap in general. Ironically, I have EMC2 talking step and direction to some Skyko controller cards (no longer being made) that control large brushless AC servo drives on a lathe. The Skyko cards have an onboard PID processor. Rutex still makes a similar card.
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