STACIS
2100 Piezoelectric Isolation System - Installation & Operation Manual
P/N 96-28765-01
Page 28 of 43
•
Adjust (reduce) the servo loop gain for the identified axis by three (3) dB, i.e. 3 clicks of the (
-
)
menu key, through the
Adjust X/Y/Z Gains
menu discussed above, and then re-assess the
performance of the system.
•
Continue to check one axis at a time to screen for any other underperforming axis by repeating the
above procedure until all instability problems are eliminated.
5.3.7 Sat./Osc. (Saturation/Oscillation) Control
This is the menu option for enabling or disabling saturation and/or oscillation control. The Saturation
Control and Oscillation Control features are advanced, non-linear, and adaptive control algorithms. They
allow the system to operate trouble-free for extended period of time under adverse conditions (periods of
high seismic noise or large payload disturbances).
Saturation Control
monitors when the signal to an HVA is in danger of saturating the actuator. To
prevent saturation, the controller automatically reduces the gain in the affected channel. Although this
preventive action also reduces the vibration isolation, it prevents a hard saturation in the servo, which can
result in unwanted impulses sent to the payload. In our experience, this is much less disruptive for most
applications. If Saturation Control reduces the gain by more than 20dB, a warning is sent over the COM
port (if enabled). If this occurs, check and remove the source of excessive external disturbance.
Oscillation Control
is a very advanced feature which monitors for oscillations in the control loops. If
oscillation is detected, this feature modifies the control system filters in an attempt to stabilize the
STACIS
®
system.
An oscillation is a consistent and high-amplitude frequency in the feedback signal. The frequency is
identified, and a filter is added to make the system more stable at that frequency. Oscillation Control
will continue to increase the aggressiveness of this filter, until the oscillation goes away. If too large a
correction was necessary to the control filters, an Alarm is triggered, and the channel is disabled.
Both Saturation Control and Oscillation Control are applied to a single axis at a time. Gain reduction in
one axis usually causes minimal changes in the system’s overall isolation performance.
•
Filtering is limited by the need for isolation. The aggressiveness of the filter is
increased through a series of 6 steps. Each increase causes a reduction in low-
frequency isolation. Beyond the 6 steps of adjustment, the loss in low-frequency
isolation is too great and the system will prompt for user intervention.
•
Oscillation control filters are not stored in FLASH memory; if the controller power
is turned OFF, the filters will all be reset to zero. If oscillation reoccurs, the filters
will re-adjust.
TMC strongly recommends that these functions remain enabled during system operation.
They may be disabled
only for diagnostic purposes
and reset to “
enabled
” once the
diagnostic is completed.
•
The setting for an individual axis is preserved once saved in NVRAM. Thus, a
disabled axis will remain disabled until the user re-enables it.
•
Even with a disabled axis, all testing (data collection, etc.) will be unaffected for the
axis.
