Page 317 - Concise Encyclopedia of Robotics

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In order for stadimetry to be accurate, the linear dimension axis (in
this case the axis that depicts the person’s height, h) must be perpendicular
to a line between the vision system and the center of the object. Also, it is
important that d and h be expressed in the same units.
See also DISTANCE MEASUREMENT.
STATIC STABILITY d = Stepper Motor
Static stability is the ability of a robot to maintain its balance while standing
still. A robot with two or three legs, or that rolls on two wheels, usually
has poor static stability. It might be all right as long as it is moving, but
when it comes to rest, it can easily fall over. A bicycle is an example of a
machine with good dynamic stability (it is all right while rolling), but
poor static stability (it will not stand up by itself when at rest).
For a two-legged or three-legged robot to have excellent static stability,
it needs a sense of balance. You can stand still and not fall over, because
you have this sense. If your sense of balance is upset, you will topple. It is
difficult to build a good sense of balance into a two-wheeled or two-
legged robot. However, it has been done, and although the technology is
expensive, it holds promise for the future.
See also BIPED ROBOT, DYNAMIC STABILITY, and INSECT ROBOT.
STEPPER MOTOR
A stepper motor is an electric motor that turns in small increments rather
than continuously. Stepper motors are used extensively in robots.
Stepper versus conventional
When electric current is applied to a conventional motor, the shaft turns
continuously at high speed. With a stepper motor, the shaft turns a little
and then stops. The step angle, or extent of each turn, varies depending
on the particular motor. It can range from less than 1° of arc to a quarter
of a circle (90°).
Conventional motors run constantly as long as electric current is applied
to the coils. A stepper motor turns through its step angle and then stops,
even if the current is maintained. In fact, when a stepper motor is
stopped with a current going through its coils, the shaft resists turning. A
stepper motor has brakes built in. This is a great advantage in robotics; it
keeps a robot arm from moving out of place if it is bumped accidentally.
Conventional motors run at hundreds or even thousands of revolutions
per minute (rpm). A typical speed is 3600 rpm, or 60 revolutions per

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