Internal Process Controls - Control of Color Imaging Systems: Analysis and Design - page 477

PE image path

CMYK

TRCs

Belt
photoconductor

Electrostatics

Level
3

Level
1

Level
2

Development
system

TC Loop

Voltage sensor

Targets

DMA sensor

Printer with
sensors (a)

Charge

Expose

Clean

Noncontacting electrostatic
voltmeter (ESV)

Fuse

Develop

Develop

Media
transport

Optical
sensor (b)

FIGURE 9.2 (a) Abstract representation of multilevel control architecture. (b) A typical
xerographic print engine with a drum photoconductor showing principal subsystems.

exposed to light. The first subsystem begins with an uncharged photoconductor and

finishes with the exposed customer page (the mirror image, also called the latent
image) expressed as a pattern of discharged dots. Therefore, the level 1 controller, in
its simple form, maintains the charge on a moving photoconductor surface at desired
set points, for both unexposed (charged) and exposed (discharged) regions. The
actuators that are normally used for controlling the photoconductor surface potential
in this process are the grid voltage, V g , and the exposure intensity, X (Table 10.3)
[5

7]. The sensor used to measure the voltage levels on the photosensitive surface is a
nonconducting electrostatic voltmeter (ESV) or electrometer; sensor examples are
available in Ref. [8]. The electrometer is generally rigidly secured to the printer,
adjacent to the moving photoconductor surface, and measures the voltage level of
the photoconductor surface as it traverses under an ESV probe before and after the

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