Notes On Commissioning - Bosch Rexroth IndraDrive MPH-02 Functional Description

9-26
Extended Drive Functions

Notes on Commissioning

Maximum Output Frequency
Delay Between Real and
Emulated Position Value
Rounding Off the Number of
Increments in Short Time
Intervals
In contrast to a "real" encoder, encoder emulation uses a simulated
encoder. In motion the real encoder signal and the output of the emulator
can differ. The causes for such differences can be:
• application errors
(e.g. inadequate wiring, exceeded frequencies, voltage drops,
incorrect programming, ...)
• systematic errors due to the technical conditions
(e.g. beat effects, position jitter, ...)
The restrictions and limits described in the following sections have to be
taken into account when encoder emulation is used.
Restrictions of Incremental Encoder Emulation
In contrast to the conventional incremental encoder for which the pulse
output frequency can be infinitely changed in fine increments (i.e. the
pulses are always assigned to fixed positions), emulated incremental
encoder signals are subject to certain restrictions which primarily result
from the digital mode of operation of the drive controller.
The maximum pulse frequency is 1024 kHz. If this frequency is exceeded,
pulses can be missing. The error message F2053 Incr. encoder
emulator: pulse frequency too high is output. A position offset of the
emulated position in contrast to the real position occurs.
I : maximum number of lines
max
n : allowed maximum speed in 1/min
max
Fig. 9-13: Calculating the maximum number of lines
Note: The max. output frequency of 1024 kHz always, i.e.
independent of the selected number of lines, has to be taken
into account for dimensioning the evaluation electronics.
Between the position detection and output of the emulated pulses there is
a delay (dead time) between real and emulated position value.
Solution:
When incremental encoder emulation has been activated (cf. P-0-0902,
bit 1,0), it is possible to activate dead time compensation in P-0-0902,
Encoder emulation control parameter with bit 3 = 1. The dead time
compensation is only effective and useful if there aren't any repeated
acceleration and deceleration processes (ideal v = constant).
In a time interval of the internal control cycle TA it is only possible to
output an integer number of increments (1 increment = ¼ line) at a time.
The remainder that cannot be output is added in the next time interval. If
there is another remainder of 0 < remainder < 1, it is added again in the
next interval etc.
This effect is the reason why the "emulated velocity" is exact on
average, but can be by a maximum of one increment too low in each of
the individual TA time intervals.
Solution:
Use the highest possible number of lines so that as many lines as
possible can be output per control cycle TA. The percentage error then is
reduced accordingly.
MPH-02, MPB-02, MPD-02
∗
f 60
=
max
I
max
n
max
DOK-INDRV*-MP*-02VRS**-FK01-EN-P