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MPH-02, MPB-02, MPD-02
Inaccuracy of Sinusoidal
Encoder Signals
Compensating Signal Shape
DOK-INDRV*-MP*-02VRS**-FK01-EN-P
The most important inaccuracies with sinusoidal signals are caused by:
• signal offset
→ the evaluated sine signal is not symmetrical to the zero line
• amplitude error
→ the signal amplitude is either too low (bad resolution) or too high
(crest range cannot be displayed)
• signal shape error
→ the curve shape differs from the exact sine shape
Actual position values are calculated from both sinusoidal signals of an
encoder that are offset by a quarter of a division period. The mentioned
errors cause sine signals differing from the ideal shape and therefore
differing actual position values compared to ideal actual position values of
exactly sinusoidal signal curves.
The controller automatically compensates the signal offset and the
amplitude error for all encoders connected to the controller.
Due to the high degree of required calculated capacity, the correction of
Errors
signal shape errors can only be activated for one of the encoders that can
be connected. To do this it is necessary to determine one encoder, for
which the correction is to be carried out, in P-0-0341, Control word for
encoder correction. The controller acquires the signal shape by
activation
of
correction values.
To acquire the signal shape errors of the encoder division periods it is
necessary to control the drive in the "velocity control" mode with a
constant velocity command value.
The following applies to the maximum velocity for determining the
correction values:
−
S
−
S
S-0-0040:
velocity feedback value
T
:
sampling time of the velocity loop
Vloop
DP/rev.:
division periods per encoder revolution (number of lines of the
rotary encoder)
DP:
length of the division period (linear encoder)
Fig. 8-30:
Maximum velocity for acquiring the encoder signals related to the
encoder shaft (rotary encoder) or the sensor head (linear encoder)
When all required measured values have been acquired, the correction
values calculated and stored in P-0-0342, Correction value table for
encoder correction, the controller completes the command execution. If
with the command C3500 being active the actual velocity value should be
lower than 50% or higher than 100% of the maximum value calculated
above, the acquisition of the encoder signals is aborted (error message
"C3501 Acquisition velocity not allowed"). For trouble-free acquisition of
the encoder signals a command value of approx. 75% of the maximum
velocity is recommended.
Note:
The values in the correction table P-0-0342 are only suitable
for the encoder for which they were determined! In case an
encoder is replaced the correction values have to be
determined again (command C3500)!
P-0-0340,
C3500
Command
, 0
03125
−
≤
0
0040
∗
T
DP
/
rev
Vloop
∗
, 0
03125
DP
−
≤
0
0040
T
Vloop
8-51
Drive Functions
Determine
encoder
(rotary encoder)
.
(linear encoder)
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