Robotics Sensors Overview

Robotics Sensors

• Sensors are like windows for robots, allowing them to perceive and measure the physical properties of their environment.
• These properties include position, orientation, velocity, acceleration, distance, size, force, moment, temperature, luminance, and weight.
• Active sensors send a signal out and measure the returned signal.
• Passive sensors simply "listen" to signals from the environment.

Sensor Attributes

• Field of view (FOV) and range: Every sensor has a specific area it can observe and the maximum distance it can reliably measure. For example, a robot needing to avoid obstacles 8 feet away requires a sensor with a range of at least 8 feet.
• Accuracy: The difference between a measured value and the actual value. A truck backing up needs accurate distance measurements for safe operation.
• Repeatability: Consistency in measurements under the same conditions. A sensor reporting a distance of 101 mm and then 102 mm under identical circumstances has a low repeatability.
• Resolution: The smallest detectable change. A sensor with low resolution might only perceive changes in whole centimeters, while a high-resolution sensor detects millimeter-level changes.
• Power consumption: Important for battery-operated robots; lower power consumption means longer operational time.

Sensor Classification

• Internal sensors: These sensors provide information about the robot itself, such as its position, velocity and acceleration.
• External sensors: These sensors gather information about the robot's surroundings. This includes cameras, range sensors, contact/proximity sensors and force sensors.

Types of Sensors

• Light Sensor(Photoresistor): Detects light intensity and creates a voltage difference; useful for light-dependent robots and solar robots.
• Sound Sensor(Microphone): Measures sound levels, generating a voltage proportional to sound intensity. Useful for robots guided by sound. Implementing sound sensors can be more complex due to the very small voltage differences compared to light sensors. It needs to be amplified to generate measurable changes.
• Temperature Sensor: Measures temperature; crucial for robots in various environments.
• Contact Sensor: Requires physical contact for triggering; typically used for obstacle avoidance. A drawback is the need for physical contact.
• Proximity Sensors: Detects presence of an object without physical contact, using methods like triangulation or time of flight. Useful alternative to contact sensors. Examples include infrared and ultrasonic sensors.
• Ultrasonic Sensor: Emits ultrasound signals and measures the time of flight for reflected waves.
• Infrared (IR) Transceivers: These sensors use infrared radiation to detect objects, movement, and distance. Active sensors emit their own infrared radiation; passive sensors react to infrared waves emitted by the environment.
• Laser Range Scanner: Measures distances by transmitting and receiving laser light; provides precise distance measurements. These are useful for larger measurement distances.
• Encoder Sensor: Measures angular position for rotary or linear motion. They translate position into code for robots using mechanical movements. Examples of 360-Degree Laser Scanning include robotic mapping. Kinect is a common example in robotics.

Sources of Error in Sensors

• Cross-talk: Two ultrasound sensors using the same frequency can not be distinguished.
• Obstacle Shape: Obstructions with complex shapes can cause inaccurate environmental perception by the robot.
• Specular Reflection: Bouncing of ultrasonic waves from multiple surfaces can lead to inaccurate distance measurements since the return signal does not only originate from the first point of contact.
• Opening Angle: Ultrasonic sensors have opening angles that lead to a range of possible positions for an object rather than precise location.

Additional Information

• Bumper Sensor: A contact sensor used to detect physical contact with an obstacle or wall. The Bumper sensor reports a value of TRUE when pressed and FALSE when released.

This quiz covers the fundamentals of robotics sensors, including their functions and attributes. Learn about active and passive sensors, their field of view, range, accuracy, and repeatability. Discover how these sensors help robots perceive and interact with their environment.