Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Mechanical limit switches are devices that sense objects by being
either directly or indirectly touched by the object. Most use a
button, lever, whisker, or slide as their local sensor. Two other types
that warrant their own categories are the magnetic reed switch and the
membrane switch, which is much like a long button actuated switch.
On a robot, the switch alone can be the whole sensor, but in most cases
the switch makes up only a part of a sensor package.
The limit switch can be thought of as a device that has at least one
input and one output. The input is the button, lever, whisker, or slide
(or for the magnetic type, anything ferrous nearby). The output is
almost always closing or opening an electric circuit. There are several
other types of limit switches whose inputs and outputs are different
than those discussed above, but only those that sense by direct contact
or use magnets will be included here. Other types are not strictly
mechanical and are more complex and beyond the scope of this book.
In a robot, there are two general categories of things that the robot’s
microprocessor needs to know about, many of which can be sensed by
mechanical limit switches. The categories are proprioceptive and environmental.
Proprioceptive things are part of the robot itself like the
position of the various segments of its manipulator, the temperature of
its motors or transistors, the current going to its motors, the position of
its wheels, etc. Environmental things are generally outside the robot
like nearby objects, ambient temperature, the slope of the surface the
robot is driving on, bumps, or drop-offs, etc. This is an over-simplified
explanation because in several cases, the two categories overlap in one
way or another. For instance, when the bumper bumps up against an
object, the object is in the environment (environmental sensing) but the
bumper’s motion and location, relative to the robot, is detected by a
limit switch mounted inside the robot’s body (proprioceptive sensing).
In this book, anything that is detected by motion of the robot’s parts is
considered proprioceptive, whether the thing being sensed is part of the
robot or not.
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