Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

266 Chapter 11 Proprioceptive and Environmental Sensing Mechanisms and Devices
These two categories subject the switch to very different problems.
Proprioceptive sensors usually live in a fairly controlled environment.
The things around them and the things they sense are all contained
inside the robot, making their shape unchanging, moving generally in
the same direction, and with the same forces. This makes them easier to
implement than environmental sensors that must detect a whole range
of objects coming from unpredictable directions with a wide range of
forces. Environmental sensing switches, especially the mechanical type,
are often very difficult to make effective and care must be taken in their
design and layout.
Mechanical limit switches come in an almost infinite variety of
shapes, sizes, functions, current carrying capacity, and robustness. This
chapter will focus on layouts and tripping mechanisms in addition to the
switches themselves. Some switch layouts have the lever, button,
whisker, or slide directly moved by the thing being sensed. Others consist
of several components which include one or more switches and
some device to trip them. In fact, several of the tripping devices shown
in this chapter can also be used effectively with non-mechanical
switches, like break-beam light sensors. The following figures show
several basic layouts. These can be varied in many ways to produce
what is needed for a specific application.
The simplest form of mechanical limit switch is the button switch
(Figure 11-1) It has a button protruding from one side that moves in and
out. This opens and closes the electrical contacts inside the switch. The
button switch is slightly less robust than the other switch designs
because the button must be treated with care or else it might be pushed
too hard, breaking the internal components, or not quite inline with its
intended travel direction, breaking the button off. It is, theoretically, the
most sensitive, since the button directly moves the contacts without any
other mechanism in the loop. Some very precise button limit switches
can detect motions as small as 1mm.
The lever switch is actually a derivative of the button switch and is
the most common form of limit switch. The lever comes in an almost
limitless variety of shapes and sizes. Long throw, short throw, with a
roller on the end, with a high friction bumper on the end, single
direction, and bidirection are several of the common types. Figure
11-2 shows the basic layout. Install whatever lever is needed for the
application.
The whisker or wobble switch is shown separately in Figure 11-3
even though it is really just another form of lever switch. The whisker
looks and functions very much like the whiskers on a cat and, like a cat,
the whisker directly senses things in the environment. This makes it