User Manual
E727T0005, valid for E-727
BRO, 2019-06-28
Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Page 119 / 240
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email
How to initialize DDL for an axis:
1.
Define a waveform using the WAV command.
2.
Optionally: Set the number of wave generator cycles to use for DDL initialization. This can be
done using the SPA or SEP command with the
DDL Repeat Number parameter
(ID
0x14000001). The factory default is 35. (To have write access to the parameter, it might be
necessary to switch to command level 1 using CCL).
3.
Not essential but recommended: Delete DDL table content which is no longer used. This can be
done using the DTC command.
4.
When the servo parameters (notch filter frequency, servo-loop P-term, servo-loop I-term and
servo-loop slew rate) have changed: Recalculate the internal DDL processing parameters using
the DPO command.
5.
Assign the waveform to the axis using the WSL command.
6.
Switch the servo on for the axis using the SVO command (closed-loop operation).
7.
Start the wave generator with the WGO command, with the "Use and reinitialize DDL" option
activated.
8.
Optionally: Check the content of the DDL table using the DDL? command.
How to use DDL for an axis:
As long as your application does not change, you can use the current DDL table content without
new initialization. In this case, start the wave generator with WGO and the "Use DDL" option
activated.
INFORMATION
If the DDL performance does not prove satisfactory or if errors occur during DDL use:
Recalculate the internal DDL processing parameters using DPO.
Reduce the frequency of the wave generator output to make sure that the axis can follow the
target values. To do this, define a new, optimized waveform with the WAV command. You can
also use the WTR command, which sets the wave generator table rate, to optimize the output
frequency.
After such changes DDL initialization must be repeated.
INFORMATION
If a phase shift between the trigger output and the actual position is observed when the wave
generator is running with the "Use DDL" or "Use and reinitialize DDL" options (actual position
measured with external device is ahead of the trigger signal), check the cut-off-frequency f
g
of the
IIR low-pass filter used for digital filtering and increase it to shorten the duration of the digital
filtering. See below for details.
The duration of the signal processing for an internal sensor results from two portions:
Duration of the analog sensor processing, which takes about 100 µs for the E-727
Duration of the digital filtering. If the
Digital Filter Type
parameter, ID 0x05000000,