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10.3.11 Alignment of the Piezo OCL Matrix OCLP
(Piezo’s Output Crosslink Matrix)
This chapter is only important for you, if you got a piezo actuator-based (PiA) or a motor AND
piezo based Aligna system (MoPiA).
In principle, the learning of the piezo OCL ("OCLP") is rather equivalent to the motor's OCL
("OCLM"). However, there are distinct differences, because the hardware behind it is quite
different: The motorized orthogonalization and the motor servo loops are completely done by
software in the microcontroller, while the piezo servo and the piezo OCL are made by hard-
ware in the BLM servo modules. (This is done for speed and precision issues, the servos can
go in principle up to MHz regions with extremely high resolution and low noise, better than
digital servos. However, this is only used and needed in very special applications.)
So one main difference is, that the matrix and servo coefficients are not just calculated num-
bers (with a very large dynamic range), but all these parameters are realized by MDACs (mul-
tiplying Digital Analog Converters), which are controlled by the microcontroller. They act like
digitally controlled potentiometers. (There are approximately 60(!) MDACs per BLM module,
up to 240(!) per Aligna rack.)
Even if the signals themselves have an "infinite" (analog, just noise limited) resolution, the
MDAC-controlled coefficients have a resolution of 14 bit (1:16192). There are a lot of sums,
differences, multiplications and divisions in the signal path. Thus, the signal heights have to be
well adapted all along the signal path, not to be too large (being clipped at the analog voltage
limits), and not too small (competing against analog offsets and noise).
Even if the piezos have a nearly infinite resolution, they have a rather small stroke, and a
rather large hysteresis of approx 5%...10% of its stroke. This makes well-defined combination
movements MUCH MORE complicated.
We offer different types and sizes of piezo actuator-based XY-scanners: The standard is the
OneInch MoPiA actuator, a compact combination of the Aligna 40 motorized mirror mount and
a 1 inch piezo-based XY actuator. In addition, there are 2 inch piezo actuators (for handling
rather heavy 2 inch mirrors of 12 mm thickness. For getting a good dynamical performance,
the 2 inch piezo actuators have an even much smaller angle stroke compared to the 1 inch
piezo actuators.
10.3.11.10 Learning of the Piezo "OCL" Matrix
The procedure is rather equivalent to the one described for the motors:
Choose "Learn Program: Piezo OCL" (The system will learn the OCL for the piezo servos)
(When you select "Learn Program: Piezo OCL", Kangoo shrinks down the motor OCL section, and
rescales the piezo OCL section.)
Click “measure Matrix!”, which starts the learning procedure:
In addition, the scaling units of the displayed position values have been blown up by selecting
"UnitsA" and "UnitsB" to "Volts, amplified for piezo". The factor is given by the parameter
"PsdPiezoAmplifA" and "...B". This is necessary to achieve a Total Matrix being the unity
matrix: The opto-mechanical system has a very small reaction (dues to small stroke of the
piezos). Thus, we need an additional gain to get the same total scaling of approx "1".
In the case of 2 inch piezo actuators this "blow-up" amplification is of the order of 30...60.
(Thus, the PSD signals seem to be very noisy and fluctuating. But this is just seemly due to
the "blown-up" measured position signals, just for the OCLP learning procedure. If you touch
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