An encoder anywhere on the ball screw would work. It's usually easier to mount an encoder on the end of a ball screw or motor shaft rather than between the motor and the ball screw. There are motors with a shaft protruding on each end and it's common practice to mount the encoder on the back shaft of the motor, with the shaft coupling to the ball screw on the other side of the motor. That's what I was discussing. There's nothing wrong with mounting the encoder on the back of the motor if you want to catch the common problem of missing pulses on a stepper motor, but an encoder on the back shaft of the motor would have no way to detect positional errors caused by a slipping shaft coupler. It would see the motor turning as commanded, and would have no way to see that the screw isn't turning with the motor because the coupler is slipping.
BTW - For very precise machines, even a large diameter ball screw is not "a solid screw". There is measurable torsional twist when accelerating and decelerating that can cause minor positional error that is significant in some precise applications. One trick that's used is to place an encoder on each end of the ball screw and detect the slight difference in rotation from one end of the screw to the other due to twisting. Some math is done to compensate for the positional error that would be caused by the twisting ball screw between the motor and the load. On 04/24/2015 08:28 PM, Joe H wrote: > Bruce, > I"m not second guessing your suggestion, just trying to educate myself. > What advantage does having an encoder mounted on the lead screw on the end > opposite of the motor have compared to mounting it anywhere else on that > screw? It being a solid screw, why would it matter? ------------------------------------------------------------------------------ One dashboard for servers and applications across Physical-Virtual-Cloud Widest out-of-the-box monitoring support with 50+ applications Performance metrics, stats and reports that give you Actionable Insights Deep dive visibility with transaction tracing using APM Insight. http://ad.doubleclick.net/ddm/clk/290420510;117567292;y _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
