Page 346 - Concise Encyclopedia of Robotics

Video Signal
VIDEO SIGNAL
See COMPOSITE VIDEO SIGNAL.
VIDICON
Video cameras use a form of electron tube that converts visible light into
varying electric currents. One common type of camera tube is called the
vidicon. The illustration is a simplified,functional,cutaway view of a vidicon.
Deflecting
coils
Photoconductive
screen
Electron
Incoming Electron gun
light beam
Lens Grids
Output
Vidicon

The camera in a common videocassette recorder (VCR) uses a vidicon.
Closed-circuit television systems, such as those in stores and banks, also
employ vidicons. The main advantage of the vidicon is its small physical
bulk; it is easy to carry around.This makes it ideal for use in mobile robots.
In the vidicon, a lens focuses the incoming image onto a photocon-
ductive screen. An electron beam, generated by an electron gun, scans
across the screen in a pattern of horizontal,parallel lines called the raster. As
the electron beam scans the photoconductive surface, the screen becomes
charged. The rate of discharge in a certain region on the screen depends
on the intensity of the visible light falling on that region. The scanning in
the vidicon is exactly synchronized with the scanning in the display that
renders the image on the vidicon screen.
A vidicon is sensitive, so it can see things in dim light. But the dimmer
the light gets, the slower the vidicon responds to changes in the image. It
gets “sluggish.”This effect is noticeable when a VCR is used indoors at night.
The image persistence is high under such conditions, and the resolution
is comparatively low. Compare CHARGE-COUPLED DEVICE and IMAGE ORTHICON.
See also VISION SYSTEM.

