In robotics, sensors are used for both internal feedback control and external interaction
with the outside environment. Animals and humans have similar distinct sensors. For
example, when you wake up, even before you open your eyes, you know where your
extremities are; you do not have to look to know that your arm is beside you, or that your
leg is bent. This is because neurons in the muscles send signals to the brain, and as they are
stretched or relaxed with the contracting, stretching, or relaxing muscles, the signal
changes and the brain determines the state of each muscle. Similarly, in a robot, as the
links and joints move, sensors such as potentiometers, encoders, and resolvers send signals
to the controller, allowing it to determine joint values. Additionally, as humans and
animals possess senses of smell, touch, taste, hearing, vision, and speech to communicate
with the outside world, robots may possess similar sensors that allow them to
communicate with the environment. In certain cases, the sensors may be similar in function to
that of humans such as vision, touch, and smell. In other cases, the sensors may be
something humans lack such as a radioactive sensor.
There is a huge array of sensors available for measuring almost any phenomenon.
However, in this chapter, we will only discuss sensors used in conjunction with robotics
and automatic manufacturing.