Moog Animatics SmartMotor™ Developer's Guide,Rev. L
Page 236 of 909
Position Error Value (in Motor View Window)
KA=formula
Set KA, Acceleration Feed Forward
If the SmartMotor is accelerating a mass, it will be exerting a force during that acceleration
(force = mass X acceleration), which disappears immediately on reaching the cruising speed.
This momentary torque during acceleration is also predictable, and its effects can be
programmed out with the KA (acceleration feed forward) parameter. KA can range from zero
to 65535.
It is a little more difficult to tune KA, especially with hardware attached. The objective is to
arrive at a value that will close the position error during the acceleration and deceleration
phases. It is better to tune KA with KI set to zero because KI will address this constant force in
another way. It is best to have KA address 100% of the forces due to acceleration, and use the
KI term to adjust for friction.
The PID update rate of the SmartMotor can be slowed down with the following values:
PID1 Set highest PID update rate, 16 kHz
PID2 (Default) Divide highest PID update rate by 2, 8 kHz
PID4 Divide highest PID update rate by 4, 4 kHz
PID8 Divide highest PID update rate by 8, 2 kHz
NOTE: A reduction in the PID rate can result in an increase in the SmartMotor
application program execution rate.
The trajectory and PID control calculations occur within the SmartMotor at the "sample rate"
selected by the PIDn command. Although 16 kHz (PID1) is available, 8 kHz (PID2, the default)
provides a reasonable compromise between optimum control and the SmartMotor application
program execution rate. The program execution rate can be increased by reducing the PID
rate using PID4 and PID8 in applications where the lower PID sample rate still results in
satisfactory control.
If the PID sample rate is lowered, remember that it is the basis for velocity values,
acceleration values and the PID coefficients. If the rate is cut in half, expect to do the
following to keep all else the same:
l
Double velocity
l
Increase acceleration by a factor of four
NOTE: If proper care is taken to keep the PID filter stable, the PID# command can
be issued on the fly.
Part 1: Programming: KA=formula
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