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Robotic sensors

Robots, particularly autonomous ones, need to sense the world around them. In this step, I will take you through a few of the many options available to add sensing to your buggy.

Force and touch

A robot that is designed to navigate the real world and interact with physical objects, for example by picking them up, must be able to measure the force it is applying to these objects. In some cases, it might be necessary for the robot to sense external forces exerted upon it.

Force

Force sensors are used by roboticists to measure the forces their robots, such as the robotic arm assembling mobile phones that you heard about last week, are exerting on the objects they interact with. It is important that the arm applies enough force to hold the part and not drop it, but not so much pressure that the component is damaged or crushed.

Other roboticists use force sensors to detect shocks or vibrations, to allow a robot to react and balance/stabilise itself. Mobile robots could use force sensors in navigation as well, although touch sensors are more common.

Touch

Touch sensors allow robots to detect physical interactions between their body and objects in their surroundings. Capacitive touch sensors use conductive properties to detect touches, most commonly from a human’s touch, but any object that can conduct electricity will work. Resistive touch sensors do not use electrical properties, but instead detect touches based on pressure applied to the plate. This type of sensor can allow a robot to navigate its surroundings, even if the object touching the sensor does not conduct electricity.

Detecting the environment

Robots can use measurements of the environment around them to influence their behaviour, or just to collect data for analysis.

Temperature

Temperature sensors can be used in a variety of contexts, not just as data collection for scientific experiments. A rover on Mars can use its temperature sensor to evaluate the terrain it is rolling over; if it detects a drop in temperature it can reduce the torque on its wheels to prepare for ice. A robot designed to fight fires could use a temperature sensor to direct itself towards the hottest parts of a burning building, where it will be most effective.

Light

Another detectable property of the environment is light. If a robot has different tasks to accomplish at night than in the day, it could detect decreasing light levels and change its behaviour to night mode. Changes in light can also indicate a change in surroundings; a robot designed to explore houses in disaster zones could use light sensors to help navigate around a home that has collapsed, by directing itself towards the light to get out of tight spaces.

Sound

Sound sensors act similarly to microphones, but are often attached to circuits that compare the amplitude of the sound to a threshold value, returning the result of that comparison to the robot. The higher the amplitude, the louder the noise. This could be used by a robot designed to study wildlife; detecting and following loud noises may be one of the pieces of data that is used to locate wildlife. A more complex use would be a sound sensor for speech recognition, responding to commands spoken by a user.

Chemical

Robots can also use specialised sensors to detect certain chemical properties. For example, pH sensors detect the acidity or alkalinity of the environment around a robot. Scientific robots could use this to check the quality of rivers or soil in remote places. Carbon monoxide is poisonous, and robots equipped to sense this gas can be used to monitor potentially dangerous environments where human explorers would be at risk.

Object proximity

Mobile robots have to navigate the world around them, often autonomously, and there are sensors that help them detect the proximity of other objects around them.

Infrared sensors

Infrared sensors detect changes in the levels of infrared radiation captured by the device. These changes are caused when an object (often a living thing) that is hotter than the background passes through the sensor’s field of view.

Ultrasonic distance sensors

A better sensor for robots that have to navigate around inanimate objects is the ultrasonic distance sensor (UDS). This type of sensor emits high-frequency noises that rebound off objects in the surrounding area and return to the robot. This is how bats sense the world when they are flying at night.

You are going to use a UDS in your buggy, and in the next step you will see how they work in greater detail.

Discussion

Pick one of the types of sensor you have seen in this step.

Think of another use of that sensor in robotics, from past experience or from your imagination.

Share your ideas in the comments section.

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This article is from the free online course:

Robotics With Raspberry Pi: Build and Program Your First Robot Buggy

Raspberry Pi Foundation