User guide

Xenus Plus User Guide Operational Theory
Copley Controls 24
Position Loop Gains
The following gains are used by the position loop to calculate the velocity command:
Gain
Description
Pp - Position loop proportional
The loop calculates the position error as the difference between the actual and
limited position values. This error in turn is multiplied by the proportional gain value.
The primary effect of this gain is to reduce the following error.
Vff - Velocity feed forward
The value of the profile velocity is multiplied by this value. The primary effect of this
gain is to decrease following error during constant velocity.
Aff - Acceleration feed forward
The value of the profile acceleration is multiplied by this value. The primary effect of
this gain is to decrease following error during acceleration and deceleration.
Gain Multiplier
The output of the position loop is multiplied by this value before being passed to the
velocity loop.
Position Loop Feedback
Xenus Plus supports two position feedback configurations
Single sensor. Position loop feedback comes from the encoder or resolver on the motor.
Dual sensor. Position loop feedback comes from the encoder attached to the load.
(Note that in either case, velocity loop feedback comes from the motor encoder or resolver.) For
more information, see Feedback (p. 17).
Position Loop Output
The output of the position loop is a velocity command used as the input to the velocity loop.
Position Wrap
The position wrap feature causes the position reported by the drive to “wrap” back to zero at a
user-defined value instead of continually increasing. Once set, the reported position will be
between 0 and n-1 where n is the user entered wrap value. This feature is most useful for rotary
loads that continually turn in one direction and only the position within a revolution is of interest to
the user.
With the wrap value set, relative moves will move the relative distance called for. Example: if the
wrap value is set to 1000 and a relative move of 2500 is commanded, the axis will turn 2 ½
revolutions.
Absolute moves will move the shortest distance to arrive at the programmed position. This could
be in the positive or negative direction. Moves programmed to a point greater than the wrap value
will cause an error.
To configure the position wrap feature, see the CME 2 User Guide.