Parker Hannifin
Chapter 5 Tuning - 51 -
Position Variable Overview
In a servo system, the controller uses two types of position information:
commanded position and actual position. As these positions change with
time, you can use the position values to determine if the system is positioning
as you expect.
Commanded Position
The commanded position is calculated by the motion profile routine from the
controller and it is updated every servo sampling period. Therefore, the
commanded position is the intended position at any given point of time.
To view the current commanded position, open the numeric status panel in
ACR-View, select Axis Parameters, then Current Position. The instantaneous
commanded position is shown for all axes.
Figure 33 Commanded Position
Actual Position
The actual position of the motor/load is the drive’s response to the
commanded position, and is measured with the feedback device. The profile
resulting from the actual position across time is the position response (for
more information, see Servo Response Overview o
n page 52).
To view the actual position, open the numeric status panel in ACR-View,
select Axis Parameters, then Actual Position. The actual encoder position is
shown for all axes
The difference between commanded and actual positions is called a
following error. To view the following error, open the numeric status panel in
ACR-View, select Axis Parameters, then Following Error. The following error
is shown for all axes.
If the motor is not moving, the position error is called a steady-state position
error. If a position error occurs when the motor is moving, it is called a
position tracking error.
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