ABB SafeMove2, Applications Manual, Page: 208 / 238

10.3 Servo Delay Factor and Servo Lag
System parameters Servo Delay Factor and Servo Lag
To explain what is affected by the parameters Servo Delay Factor and Servo Lag
in the SafeMove configuration (see Configure additional axes on page 147 ) it is best
to consider an example.
In graph (a) in the figure below, the Servo Delay Time is illustrated using a
constructed example where a reference and a corresponding measured angular
motor position is shown. The corresponding
Servo Delay Factor can be computed
using:
Servo Delay Factor = Servo Delay Time / 4
In graph (b) in the figure below, the Servo Lag parameter is illustrated when the
measured signal is shifted with the Servo Delay Time . The measured position
should now be within a distance of +/- Servo Lag from the reference at every time
instance. If the measured position is outside the specified region the SafeMove
position supervision is triggered.
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angle
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Servo Lag
(a) (b)
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Figure 10.1: Illustration of Servo Delay Time (a) and Servo Lag (b). Solid line is motor angular position
reference (test signal 17) and dashed is the corresponding measured motor angular position (test signal
18). In (b) the measured motor angular position signal is shifted Servo Delay Time in order to illustrate
that it is the time shifted signal (samples) that should lie /- Servo Lag radians from the reference.
Note
The signals in the figure are only for illustrative purpose. The Servo Delay Time
in a real system is small, typically in the range 12-16 ms, which means a Servo
Delay Factor in the range 3-4. If the Servo Delay Factor is incorrect the Servo
Lag has to compensate this since the difference between reference and measured
motor angular position will be large when the axis accelerates, runs at high speed,
or decelerates.
Continues on next page
208 Application manual - Functional safety and SafeMove2
3HAC052610-001 Revision: P
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10.3 Servo Delay Factor and Servo Lag