11-15-2004, 05:38 PM
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| | | Join Date: Oct 2003 Location: Sweden Age: 34
Posts: 398
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Originally Posted by WoodSnarfer Awesome post, thanks! So, what design choices can the would-be router designer make ahead of time to minimise the chance of servo ringing? Is it simply a wise choice of motor (i.e., matched to the load & speed demands of the axis) -- or does the Gecko handle it for us -- or does Mach2 (or some other software) handle it for us?
Thanks,
Chris |
The way acceleration and deceleration is handled is up to the controller (Mach2 for instance). You won't get oscillations by setting these wrong, but S shaped acceleration is easier on the mechanics than constant/linear acceleration.
PID parameters are set in the servo driver (e.g. the Gecko drive). Get these wrong, and you might get very nasty oscillations (vibrations) from the motor. These will wear out the mechanics quicky - and sound awful! This is the "not enough D or too much P" part described by Mariss.
(Mostly to Allen): PID adjustments are done to get the machine to respond as quickly and accurately as possible to a command, while still making sure the machine is stable (no oscillations). First the difference between actual and commanded values are calculated (= error), then a control signal is calculated as the sum of proportional (= factor * error), integral (= factor * sum of all errors measured from machine start), and derivative (= factor * rate of change of error) terms. The three factors are the things one adjusts (usually called Kp, Ti, Td). It can be quite difficult to get them right.
Arvid  |
)and I appreciate it.
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