Page 388 - Sensors and Control Systems in Manufacturing

342
Se v e n
Cha p te r

0.20
Nonlinearity (%) ILS

0.05
0

20 40 60 80 100 120 140
Displacement (μm)

FIGURE 7.17 The linearity of a conventional capacitive position sensor system
versus ILS (Integrated Linearization System), shown before digital linearization.

controllers. Figure 7.18 shows the linearity of a piezo flexure nano-
positioning stage with an integrated capacitive position sensor operated
in closed-loop mode with an analog controller. All errors contributed
by the mechanics, PZT drive, sensors and electronics are included in
the resulting linearity of better than 0.02 percent. Even higher linear-
ity is achievable with digital controllers.
The long-term stability of the nano-capacitive position sensor
and electronics design is shown in Fig. 7.19. They enable direct
measurement of the moving platform and are especially well-suited
for multiaxis measurements in parallel metrology configurations.
Parallel metrology means that the controller monitors all controlled
degrees of freedom relative to “ground,” a prerequisite for active tra-
jectory control. The capacitive sensors also provide high linear accuracy.

10
8
6 4
Deviation Δx/nm –2 2 0

–4
–6
Forward
–8
Backward
–10
0 1 2 3 4 5 6 7 8 9 10
Input/V
FIGURE 7.18 Linearity of a 15-µm piezo nano-positioning stage operated with
advanced control electronics.