Project 06/2005
Danaher
Motion
3.13.1. Standard Position Loop
Position loop is the standard operating mode of the SERVO
STAR
system.
For position operation, set the position loop gain to a value greater than zero.
Typically, you set up the position loop using
MOTIONLINK
. See the
SERVOSTAR
®
MC Installation Manual
for more information.
3.13.2. Dual-feedback Position Loop
Dual-feedback position loop compensates for non-linearity in mechanical
systems (inaccuracy from gears, belt drives, or lead screws, or backlash
from gears and lead screws). Dual-feedback position loop adds a second
feedback sensor (usually a linear encoder) to the system so the load position
is directly determined. Unfortunately, the load sensor cannot be the sole
feedback sensor in most systems. Relying wholly on the load sensor usually
causes machine resonance that severely affects system response. Dual-
feedback position loop forms a compromise: uses the load sensor for
position feedback (accuracy is critical) and uses the motor sensor for velocity
feedback (low compliance required). This is the dual-feedback position loop
shown below.
The additional hardware for dual-feedback position loop is a second encoder
connected to the drive which is running dual-feedback position loop. You
configure the drive for dual-feedback position loop operation using
MOTIONLINK
. See the
SERVOSTAR
®
MC Installation Manual
for more
information. The SERVO
STAR
MC does not close the servo loops and is not
directly involved in dual-feedback position loop operation. In a sense, the MC
is not aware that the drive is operating in dual-feedback position loop.
However, when setting up the feedback system, you must configure your
units for the external encoder, not the motor feedback device. In addition,
you must also tell the MC to monitor the external encoder for position error.
This is done with
<axis>.FEEDBACK
. For example:
A1.Feedback = External 'Set the axis feedback to the load
82 Rev
E
M-SS-005-03l
