Baumuller b maXX BM2500, Operating Manual

Page: 170 / 822

Configuration
Parameter manual b maXX BM3000
Document no.: 5.12001.07 Baumüller Nürnberg GmbH
170
of 820
4.4
4.4.6.5 Encoder accuracy and excentricity
To increase the absolute accuracy in the drives and to reduce the vibrations at rotational
frequency the encoder angle can be improved by an angular-dependent correction value.
Vibrations may occur in the speed, with the frequency of the present speed, if the encoder
is not exactly aligned centrically towards the motor shaft. The position error, which was
caused by an encoder eccentricity, cannot be corrected by the positioning controller or by
the speed controller. The position error can be approximated by a sinusoidal function.
Thus, the control error is suppressed on the encoder angle by adding an additional angle
with a sinusoidal function.
Encoders providing a low resolution such as resolvers are imprecise in their absolute ac-
curacy. In the controller the basic vibration (1st harmonic vibration) as well as other har-
monic (up to the 4th harmonic vibration) angular displacements can be compensated. For
this purpose the amplitude and the phase of the correction function must be entered in
Z
106.71
–
and
Z
106.70
–
(basic vibration) and in
Z
106.76
–
and
Z
106.77
–
(higher har-
monic vibrations). The maximum harmonic vibration to be corrected is specified by
Z
106.75
–
whereat 0 is the 1st harmonic vibration. The correction is enabled by bit 6 of
Z
106.3
–
.
Figure 87: Encoder excentricity
Determination is carried out in current control. The setpoint frequency (speed) must be
constant. It must lie between 0.1 and 500 Hz.
0
2
p
t
t
0
2
p
0
a)
b)
5000_0231_rev02
0
2
p
0
2
p
0
a)
b)
Encoder excentricity
Phase shifting 106.70
Encoder excentricity
a 106.71 mplitude
Position actual
value 106.10
(angle)
Position actual
value 106.10
(angle)
Position
deviation
angle
18.61
Approximation
2
p
a) Error of encoder excent ricity and its approach
b) Variation of the position value angle