6.2 Dual-Servo Stage
6.2.5 Some Concluding Comments
amplifi cation ratio have been evaluated through experiment and FEA. For the coarse positioning stage, a sliding mode controller with the feed-forward friction compen- sator was designed to consider parameter variation. In the fi ne motion stage, the Preisach model–based feed-forward compensator integrated with PID feedback con- troller was established to effectively remove the residual position error after coarse positioning. These controllers were experimentally realized in a decentralized man- ner to avoid the coupling effect. It has been demonstrated through controller imple- mentation that the smart dual-servo system has the accuracy of ±200 nm for 1 mm step movement, and ±5 μm for the sinusoidal trajectory tracking. The control results presented in this section are quite self-explanatory, justifying that the control system featuring two smart material actuators, ER clutch and piezostack, can offer a desir- able motion range with high positioning accuracy.
0.0 0.4 0.8 1.2 1.6
Displacement (mm)
Time (s)
Desired Macro motion Dual servo motion
–3 –2 –1 0 1 2 3
Input field (kV/mm)
Time (s) (a)
–20 0 20 40 60 80
Displacement (μm)
Time (s)
–2 –1 0 1 2 3 4
Input voltage (V)
Time (s)
(c) (d)
0.90 0.95 1.00 1.05
Macro off Micro on
Displacement (mm)
Time (s)
Desired Macro motion Dual servo motion
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
2.0 2.5 3.0 3.5 4.0 –9002.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 –600
–300 0 300 600 900
Error (nm)
Time (s) (e)
(b)
(f )
FIGURE 6.20 Robustness investigation of smart dual-servo system (regulating). (a) Dual- servo and macro motion, (b) input for the coarse stage, (c) fi ne stage displacement, (d) input for the fi ne stage, (e) displacement after 2 s, and (f) error signal. (From Han, S.S. and Choi, S.B., Proc. Inst. Mech. Eng. Part C J. Mech. Eng. Sci., 218, 1435, 2004. With permission.)
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–1.2 –0.9 –0.6 –0.3 0.0 0.3 0.6 0.9 1.2
Displacement (mm)
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7 Application to Hydraulic Control System
7.1 PIEZOACTUATOR-DRIVEN PUMP