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6-16 Operation
MN1928
The remaining gain terms are
Velocity Feed forward
(
KVELFF
) and
Acceleration Feed
forward
(
KACCEL
) described below.
In summary, the following rules can be used as a guide:
H
KPROP: Increasing KPROP will speed up the response and reduce the effect of
disturbances and load variations. The side effect of increasing KPROP is that it also
increases the overshoot, and if set too high it will cause the system to become unstable.
The aim is to set the Proportional gain as high as possible without getting overshoot,
instability or hunting on an encoder edge when stationary (the motor will buzz).
H
KVEL: This gain has a damping effect on the whole response, and can be increased to
reduce any overshoot. If KVEL becomes too large it will amplify any noise on the velocity
measurement and introduce oscillations.
H
KINT: This gain has a de-stabilizing effect, but a small amount can be used to reduce any
steady state errors. By default, KINTMODE is always on (mode 1).
H
KINTLIMIT: The integration limit determines the maximum value of the effect of integral
action. This is specified as a percentage of the full scale demand.
H
KDERIV: This gain has a damping effect dependent on the rate of change of error, and so
is particularly useful for removing overshoot.
H
KVELFF: This is a feed forward term and as such has a different effect on the servo
system than the previous gains. KVELFF is outside the closed loop and therefore does
not have an effect on system stability. This gain allows a faster response to demand
speed changes with lower following errors, for example you would increase KVELFF to
reduce the following error during the slew section of a trapezoidal move. The trapezoidal
test move can be used to fine-tune this gain. This term is especially useful with velocity
controlled servos
H
KACCEL: This term is designed to reduce velocity overshoots on high acceleration
moves.
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