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, stretch, or relaxed 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.