Image Processing Reference
In-Depth Information
The model-based curves for a typical electrostatic system are shown at a nominal
operating point in Figure 9.5a through c with notations V
go
¼
U
go
, X
lo
¼
U
lo
,
V
g
¼
U
g
, X
¼
U
l
. Figure 9.5a and c plot photoconductor potentials as a function of
the grid voltage for the unexposed and exposed regions, respectively. Figure 9.5b is
basically a laser power curve, a photo induced discharge curve (PIDC) at the fully
charged photoconductor potential. Points on these
indicate a
nominal operating point (chosen at random to illustrate the approach). V
ho
and V
lo
are
voltages at the nominal operating point
gures marked by
x
''
''
When there is no feedback, V
ho
is
the voltage on the unexposed photoreceptor, for the grid voltage set to V
go
.Withthe
grid voltage remaining at V
go
, if the laser power is set equal to X
lo
, then the photo-
conductor will be exposed to V
lo
volts (shown in Figure 9.5b).
Let b
11
be the slope of the curve in Figure 9.5a at the point marked
x.
''
''
''
x
''
at
{V
go
, V
ho
}. Let
D
U
g
(used synonymously with ul
g
in Figure 9.4) be the deviation
around V
go
which would be generated by the controller when the charging control
loop is closed. Let b
22
be the slope of the curve at point
in Figure 9.5b that has
the coordinates {X
lo
,V
lo
}. Similarly, let b
21
be the slope of the curve at point
''
x
''
''
x
''
in
Figure 9.5c that has the coordinates {V
go
, V
lo
}. Let
D
U
l
(used synonymously with ul
l
in Figure 9.4) be the deviation about X
lo
, caused by the electrostatic controller. The
expressions for the deviations in photoreceptor voltages,
D
V
h
and
D
V
l
, can be written
in terms of the small signal deviations {
D
U
g
,
D
U
l
}{u
g
, u
l
}, as follows:
D
V
h
¼
b
11
D
U
g
D
V
l
¼
b
21
D
U
g
þ
b
22
D
U
l
(
9
:
22
)
-450
-500
-550
V
ho
X
-600
-650
V
go
=U
go
-700
-700
-680
-660
-640
-620
-600
-580
-560
-540
-520
-500
(a)
V
g
=U
g
(volts)
FIGURE 9.5
(a) V
g
(U
g
)
V
h
curve gives slope b
11
at point
''
x.
''
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