Page 253 - Concise Encyclopedia of Robotics

Presence Sensing
Fuses and breakers
Ifa fuse blows, it must be replaced with another of the same rating. If the
replacement fuse is rated too low in current, it will probably blow out
right away, or soon after it has been installed. If the replacement fuse is
rated too high in current, it might not protect the equipment.
Circuit breakers do the same thing as fuses, except that a breaker can be
reset by turning off the power supply,waiting a moment,and then pressing
a button or flipping a switch. Some breakers reset automatically when the
equipment has been shut off for a certain length of time.
Safety issues
Power supplies can be dangerous. This is especially true of high-voltage
circuits, but anything over 12 V should be treated as potentially lethal. In
all AC-operated electronic apparatus, high voltage exists at the input to
the supply (where 117 V appears). A CRT display has high voltages that
operate its deflecting coils.
A power supply is not necessarily safe after it has been switched off.
Filter capacitors hold a charge for a long time. In high-voltage supplies of
good design, bleeder resistors are connected across each filter capacitor, so
the capacitors will discharge in a few minutes after the supply is turned
off. But don’t bet your life on components that might not exist in a piece
of hardware, and that can sometimes fail even when they are provided. If
you have any doubt about your ability to repair a power supply, leave it to
a professional.
See also ELECTROCHEMICAL POWER and SOLAR POWER.
PRESENCE SENSING
Presence sensing is the ability of a robot or other machine to detect the
introduction of an object into the environment. Such a device can make
use of bumpers, whiskers, visible light, infrared (IR), or acoustic sensors.
Bumpers and whiskers
The simplest presence sensors operate by direct physical contact. Their
output is zero until they actually hit something. Then the output rises
abruptly. Bumpers and whiskers work this way.
A bumper might be completely passive, making the robot bounce
away from things that it hits. More often, a bumper has a switch that
closes when it makes contact, sending a signal to the controller causing
the robot to back away.
When whiskers hit something, they vibrate. This can be detected, and
a signal sent to the robot controller. Whiskers might seem primitive, but

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