Aligna
®
4D User Manual
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Note: The "PosOK" threshold is given in the unit "Volts". Thus if the displayed units in the XY
display is "mm" or anything different from "Volts", and the scaling of detector A and B are
different, "PosOK" will be displayed as TWO rectangles (of two different green colours), corre-
sponding to the two different scaling values of A and B.
"MotorWrk" defines the threshold for activating motor servo work. (It is used when only mo-
torized actuators are enabled.)
If the (four) error values (Ax, Ay, Bx, By) are below this threshold, the motors will stay at rest.
The reason is: Very small or very fast pointing fluctuations cannot be compensated for by the
motors (which have a very small, but not infinite fine mechanical resolution, hysteresis, etc.)
(See explanation of "LowPass"!)
The "Motor Work" threshold is indicated in the XY display as a red rectangle.
"ErrHyst" (Error Hysteresis [%]) is an extension of "MotorWrk": If this hysteresis is set to 0
(inactive), the motors will work if one of the errors is above "MotorWrk" threshold. The motors
will not work if all are within the given value. However, this leads to following behavior: Some-
times this "MotorWrk" threshold has to be selected rather high (at high shot-to-shot noise, e.g.).
Well, if the servo starts movement to the target position, but it will stop, when the threshold is
reached, it will not reach the really target position, but remains at the border of the threshold. It
starts working very soon, if the border is overcome by any small noise peak.
If the hysteresis value is chosen as "90%", e.g. the servos will work until all errors are within
10% of the MotorWork threshold (thus much closer to the target position). Then the motors
remain in rest, until the (100%) threshold has overcome.
This leads to a closer pointing to the target pointing without permanently switching the motors
on and off.
In the XY display the inner hysteresis MotorWork threshold is displayed as a dark red rectan-
gle, the outer hysteresis (which IS the MotorWork) is indicated as a red rectangle, as ex-
plained before.)
"MoPiA" Threshold is used in "MoPiA mode" (motorized AND piezo actuators). The piezo
servos are always working (even at infinitely small errors), because the servos have an "infi-
nitely" high resolution. They will work with rather high speed for compensation of fluctuations
and mechanical vibrations. However, the piezos have a limited, small stroke. Even rather small
drifts will drive the piezos to their limits. Thus, the motorized servos will keep the piezo outputs
close to their mid positions. If the piezos remain in their mid positions, the motorized actuators
will keep in rest to achieve less noise by moving the mirrors.
The "MoPiA" threshold defines the piezo servo output values (deviation from zero), when the
motor servos will start working.
The "MoPiA" threshold is indicated in the XY display as a blue rectangle
10.3.8 "Hidden Parameters" Section
In section "hidden parameters" are some parameters which are not normally used, or which
are set automatically. They are available for debugging purposes.
((They will be described in a later version of this manual.))
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