IR Reflective

In an IR reflective existence sensor, an IrED shines IR to a location where a wall may exist, then a phototransistor picks up any reflected IR (if a wall does exist). IR reflective existence sensors are also called look-down sensors because they are typically placed on ``wings'' that glide over the top of walls.

This type of sensors is the oldest type and also the most commonly used due to they simplicity. They are prone to problems such as vibration (of the wing) because reflective sensors are optimized for detecting reflection at a certain distance. If the sensors are too far or too close to a surface, they may not register reflectance.

Reflective sensors can be used to detect walls that are not immediately around the robot. By maximizing the width of the sensor wings, reflective sensors can sense walls on the other side that are perpendicular to the direction of motion. Refer to 13.2 for a typical configuration of IR reflective existence sensors.

Figure 13.2: Configuration of IR reflective sensors

$$\includegraphics{robot-ir-reflect}$$

Reflective sensors are also very helpful in rotation error detection because they can be used to align the direction of the robot during a turn.

It is probably a good idea to at least prepare a robot to use this type of sensors as a plan B. Even if you have ideas of using much better sensors, it is still safer to make sure the robot can switch to use this type of sensors in case things do not work out as expected.