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B.2 Control system operation
The following sections describe the operation of the position, speed and torque controllers.
B.2.1 Position controller
The position controller, shown below, is a typical proportional + integral + derivative (PID)
controller, with gains set by the Mint keywords KPROP, KINT and KDERIV. The position
demand from the profiler is compared with the measured position and the error is fed into the
PID control calculation. The resulting value forms the basic speed or torque demand,
depending on the CONFIG setting. The effect of the integral term can be changed using the
KINTLIMIT and KINTMODE keywords. KINTLIMIT sets the maximum value of the effect of
integral action, as a percentage of the full scale demand. KINTMODE can be used to specify
the circumstances under which the integral term is applied.
As an alternative to the derivative term, a velocity feedback term is available by setting
keyword KVEL.
To improve the tracking performance of the position controller, the profiler speed is fed forward,
by gain KVELFF, to give a contribution to the final speed or torque demand. The profiler
acceleration is fed forward by gain KACCEL to give a contribution to the final speed demand.
The position control calculation is performed every 500μs.
The gain values KPROP, KINT, KDERIV, KVEL, KVELFF and KACCEL must be tuned for each
application. This can either be performed automatically within the Commissioning Wizard, or
manually using the Fine-tuning tool in Mint WorkBench.
Profiler speed
(VELDEMAND)
Profiler position
(POSDEMAND)
+
-
B-6 Control System
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Velocity feedforward term
KVELFF
Proportional gain term
KPROP
Following
error
Integral gain term
(FOLERROR)
dt
Derivative gain term
d
KDERIV
dt
Figure 54 - Position control system
+
+
+
+
KINT
+
-
Velocity feedback
term
KVEL
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Speed demand
Measured speed
(VEL)
Measured position
(POS)
MN1902
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