Too high a gain?
On my systems I use the following,
I set the KP, KI & KD by starting with low or zero KI, set proportional gain KP to a low value = 1 and KD =100.
Test a move and increase KD until motor vibrates, then reduce slightly, next increase the value of KP, the error on the test move will reduce untill the motor starts to vibrate, then back off.
Finally KI is increased to improve the in-position error.
You may need to go back and forth with minor adjustments, before it is complete.
But if you have a system where the motor/load inertia is not matched properly, you may find you only get satisfactory results at low accel/decel settings.
I use this pattern to really put the motion commands to the limit.
http://www.cnczone.com/forums/showthread.php?t=57695
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.