Parker Products ViX250AE - Manual (Page 63)

VIX AE SERVO DRIVE USER GUIDE 56
also serves to average the effects of the digital control loop, reducing the jitter at standstill
and the audible noise. The value of FT should be kept as low as possible. The arbitrary
units used to set the value of FT cannot be directly related to any time value.
GF Description
The opposing action of proportional and velocity gains result in a position error which
depends on speed. This is called ‘following error’. Feedforward gain can be used to offset
the following error and improve tracking accuracy. This is important in contouring
applications.
GI Description
Proportional action may be insufficient to overcome static position errors caused by
gravitational load effects. Integral action accumulates a steady state error until sufficient
torque is produced to move the load. It improves overall positioning accuracy but may
produce low frequency oscillation around the commanded position.
GP Description
Proportional gain determines the amount of torque produced in response to a given position
error. It sets the stiffness of the system and affects the following error. A high proportional
gain gives a stiff, responsive system but results in overshoot and oscillation that require
damping.
GV Description
Velocity feedback is a signal which increases with shaft speed. It acts in a negative sense
opposing the proportional action and helping to stabilise the motion. The damping action of
velocity feedback allows a higher proportional gain to be used.
IC Description
System variable IC sets the configuration of the drive’s brake input circuit – see ‘Brake Input
Circuit’ in the Electrical Installation section.
IM and IW Description
Integral mode determines when integral action (GI) is applied, either continuously or within a
integral window defined by IW.
IX Description
System variable IX determines the position of the index pulse relative to phase U
(or phase 1) of the drive. Altering the position of the index pulse allows compatibility with
different motor types. Incorrect settings will result in uncontrollable motion.
PA Description
PA reports the actual position of the motor shaft. Although PA is marked as being read only
it will accept the value 0 to be written to it for resetting purposes. If you perform a W(PA,0)
system variables PF, PE and PT will also be set to 0. However, if you immediately perform a
read of these system variables non-zero values will be reported due to normal servo action.