On Thu, 2011-02-03 at 15:16 +0200, Slavko Kocjancic wrote: > That's not problem of friction at all!. > > The worst you have is 'sticky' axis. > That means you need a lot more power to start to move axis and when already > moving the required power is a way smaller. > And if that ratio is big then tuning PID is near imposible. You can have low > static error or low (or none) overshots but not the both!. > So in this point of view the mechanics is bad nad electronic's can't do the > job. > The ratio can be measured with spring scalle. > Just make arm on screw and then pull that arm with scale. Slowly pull until > axis move then stop pulling and you have reading just at the point before > start and when stoped. (you need some support for pulling as if you pull > with bare hand then the 'stop' can't be measured as hand is to 'springy') > And if ratio is biger than 1:2 then you have serrious problem.
One can see these forces if you use an oscilloscope to look at the current going to the axis motor. If there is stiction the current will quickly spike then fall at the start of a move command. If there is a delay then a spike, there is flex or backlash. I would look at the maximum motor RPM, decide on an maximum joint rate, then set up a pulley ratio to match, so that the motor has the maximum mechanical advantage. Another thing that comes to mind. C=pi*D=3.14*6"=18.85" 2min/360deg=2/21600=0.00009259 0.00009259*18.85=0.001745" So if the table is accurate to 2min, at 3" from the center, the linear accuracy is close to 0.0017". I would tend to hope for better accuracy. It would be interesting to put an indicator on a post at a 3" radius and see what a 10 degree command produces. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
