Drive Configuration
Initial Setup of the Register Tree
5.2.3 Axis[].Parameters.PathPlanner
This node contains the parameters relevant for the internal path planner. These parameters do not in-
fluence the trajectory generation of an external control system like
TwinCAT
. Nevertheless, the parame-
ters need to be set to reasonable values as the internal path planner is used for testing of the controller
loop and also for some moves commanded by the external control system (e.g. homing moves). More-
over the setup of the modulo values need to be in accordance with the setup of the external control
system (e.g. TwinCAT).
ModuloPositionMaximum
and
ModuloPositionMinimum
: If the axis does not require a modulo mo-
tion, which is the normal case if an axis is not a spindle, both values are set to zero. Modulo motion
is typically required for spindles with long running velocity moves and without a restriction of the
move range. For example a typical setting for the modulo range with position unit in radian is:
ModuloPositionMaximum
= 6.283185307179586476925286766559 (= 2π)
ModuloPositionMinimum
= 0.0
The dynamic settings of the path planner depends on the mechanical and electrical properties of the
axis and on the requirements of the process. The following inequations may help to estimate reason-
able upper limits for the settings:
u
max
>
JL
K
t
r
max
+
JR
K
t
a
max
+
K
v
v
max
i
max
>
J
K
t
a
max
+
T
ext
Maximal velocity
v
max
[rad/s]
Inductance of the motor
L
[H]
Maximal acceleration
a
max
[rad/s
2
]
Inertia of the rotor
J
[kg m
2
]
Maximal jerk
r
max
[rad/s
3
]
Induced voltage constant
K
v
[Vs/rad]
Maximal current
i
max
[A]
Moment-current constant
K
t
[Nm/A]
Maximal voltage
u
max
[V]
External torque
T
ext
[Nm]
Resistance of the motor
R
[
W
]
For DC motors the maximal voltage is given by the DC bus voltage and for AC motors by the DC bus volt-
age divided by square root of three. The inequations above are simplified.
PositionMaximum
and
PositionMinimum
: Set soft limits for the stroke of the axis. If the axis does
not require soft limits, both values are set to zero. Values other than zero enable the following be-
havior.
If a move command such as
MoveAbsolute
targets a position outside the limits, the move is re-
jected with an error message.
If the axis is in coupled motion and the control system runs out of limit, the axis will throw an er -
ror at the soft limit position and trigger an emergency stop.
If the axis already is outside the limits, only move commands towards the legal side are allowed.
The same applies to coupled motion, with the following restrictions.
If the position is higher than
PositionMaximum
, the velocity must be negative
.
If the position is smaller than
PositionMinimum
, the velocity must be positive
8 The DirectCoupledMotion state expects valid triplets of Position-Velocity-Acceleration data. In the illegal case where triplets contain
velocity=0, the software limit feature will not work properly.
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