Page 59 - Concise Encyclopedia of Robotics

Charge-Coupled Device (CCD)
the controller, stores those instructions, and then carries them out inde-
pendently of the central controller.
In some robotic systems, the individual units are completely and con-
tinuously dependent on the central controller, and cannot function if the
communication link is severed. Such a system is said to employ fully cen-
tralized control. Compare DISTRIBUTED CONTROL.
See also AUTONOMOUS ROBOT and INSECT ROBOT.
CHAIN DRIVE
A chain drive is a method of transferring mechanical energy in a robotic
system from an actuator to a manipulator or end effector. It can also be
used in wheel-drive propulsion systems. The system consists of a chain
and a set of wheels with sprockets.
The main asset of the chain drive is its simplicity. It can provide addi-
tional traction compared with a cable drive, because the chain is not likely
to slip on the sprockets. Another asset is the fact that variable speed and
power can be obtained by using sprockets of various sizes, in conjunction
with a shifting mechanism. On the downside, the chain can come off the
sprockets. The chain requires lubrication and maintenance, and can be
noisy in operation. A common example of a chain drive is found in any
bicycle. Compare CABLE DRIVE.
CHARGE-COUPLED DEVICE (CCD)
A charge-coupled device (CCD) is a camera that converts visible-light
images into digital signals. Some CCDs also work with infrared (IR) or
ultraviolet (UV). Common digital cameras work on a principle similar to
that of the CCD.
The image focused on the retina of the human eye, or on the film of
a conventional camera, is an analog image. It can have infinitely many
configurations, and infinitely many variations in hue, brightness, con-
trast, and saturation. A digital computer, however, needs a digital image
to make sense of, and enhance, what it “sees.” Binary digital signals have
only two possible states: high and low, or 1 and 0. It is possible to get an
excellent approximation of an analog image in the form of high and
low digital signals. This allows a computer program to process the
image, bringing out details and features that would otherwise be impos-
sible to detect.
The illustration is a simplified block diagram of a CCD. The image
falls on a matrix containing thousands or millions of tiny sensors. Each
sensor produces one pixel (picture element). The computer (not shown)
can employ all the tricks characteristic of any good graphics program. In

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