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154 CHAPTER 4. DEMONSTRATION EXAMPLES
Figure 4.3: Schematic diagram of the JPL Phase B optical testbed design problem
problem is the fact that the voice-coil mirror assembly has significant mass and its
movement excites a mode in the structure. An identically driven counterbalance
effectively makes the piezo-electric actuator reactionless.
The closed loop design problem is illustrated in Figure 4.4.
Figure 4.4: JPL Phase B closed loop optical control configuration
We now construct a model of the voice-coil mirror actuator, vcmodel. This model has
been obtained from identification experiments. Note that it has an oscillatory pole pair
at a frequency very close to an oscillatory zero pair.
vcmodel1 = makepoly([1,.056309,1162.8],"s")/...
makepoly([1,.78756,1189.1],"s")
vcmodel2 = -252861.0/makepoly([1,1.0936,19.673],"s")
vcmodel = vcmodel1*vcmodel2
delete vcmodel1 vcmodel2
size(vcmodel)?
ans (a row vector) = 1 1 4
In the frequency range of interest the piezo mirror driver can nominally be modeled as a