A robot vacuum maps a room by turning sensor data into a useful picture of its surroundings. This matters because the robot must clean efficiently without crashing into furniture, falling down stairs, or missing large areas of the floor. Mapping lets the machine plan routes instead of wandering randomly.
The same engineering ideas are used in warehouse robots, drones, and self-driving vehicles.
Key Facts
- Distance from time of flight: d = vt/2, where v is wave speed and t is round-trip time.
- Wheel odometry estimate: distance = wheel circumference x rotations.
- Pose means the robot position and direction, often written as (x, y, theta).
- SLAM means simultaneous localization and mapping, where the robot builds a map while estimating its own pose.
- An occupancy grid stores each small cell as likely free, occupied, or unknown.
- A planned cleaning path often balances coverage, obstacle avoidance, battery use, and return-to-dock distance.
Vocabulary
- SLAM
- SLAM is a method that lets a robot build a map of an unknown space while also figuring out where it is in that map.
- Lidar
- Lidar is a sensing system that uses laser light to measure distances to walls, furniture, and other objects.
- Odometry
- Odometry is the process of estimating a robot's movement by measuring wheel rotation or motor motion.
- Occupancy Grid
- An occupancy grid is a map made of small cells that records which areas are likely open, blocked, or unexplored.
- Path Planning
- Path planning is the process of choosing a route that lets the robot reach goals while avoiding obstacles.
Common Mistakes to Avoid
- Assuming the robot knows the room perfectly at the start is wrong because it must collect sensor data over time and update its map as it moves.
- Treating wheel odometry as exact is wrong because wheels can slip, carpets add drag, and small rotation errors build up into large position errors.
- Ignoring sensor range limits is wrong because cameras, lidar, bump sensors, and cliff sensors only detect certain features at certain distances and angles.
- Thinking mapping and cleaning are the same task is wrong because mapping estimates the environment, while cleaning path planning decides where the robot should travel next.
Practice Questions
- 1 A lidar pulse returns to the robot after 20 ns. If light travels at 3.0 x 10^8 m/s, how far away is the wall using d = vt/2?
- 2 A robot wheel has a circumference of 0.20 m and turns 45 times while driving straight. Estimate how far the robot traveled if there is no slipping.
- 3 A robot vacuum sees the same chair leg from two different positions, but its wheel odometry suggests the chair leg should be in two different places on the map. Explain how SLAM can use this repeated observation to correct the map and the robot's estimated position.