This discussion of servo gear heads brings up an interesting question for me.
I've been working on a system that has a CANopen controller Step/Servo with integrated encoder. The motor turns a lead screw (10 TPI) which moves a scissor jack type mechanism. We have an extra external encoder mounted on the screw to be able to determine where the screw is on power up since it could be anywhere. The step/servo is configured to have 200 steps per rev which still works out to 0.0005" of linear movement. More than accurate enough. What we're finding is that occasionally, a CAN message with a Move to Position command of 2549 steps moves one or two less steps than it should. To position 2547. The status CANopen message does not report move complete. Our software times out waiting for that move complete message after 15 seconds. The actual move up to that position is only 4 seconds. So the step/servo has over 10 seconds to move 1.8 to 3.6 degrees (2 steps) to reach the end of move position. I've been told to ignore this and when the external encoder is close enough go on with the rest of the motion profile. In other words, ignore that the motor isn't reaching the target position. If I allowed my Electronic Lead Screw to not always reach the end position I think I'd have users complaining. The process isn't severely compromised by that two step shortfall. So we can go on by ignoring motion complete. But this has all the appearance of something that will fail worse later on if not addressed. Am I being too fussy? Thanks John _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
