How do Vacuum Robots actually work?

Vacuum robots are one of the coolest home gadgets out there! Like, imagine a creature going around your place without any remote control and on its own. Let’s see how it works in short before we get into the nitty-gritty details.

The vacuum robot uses powered wheels to move around autonomously and has a vacuum pump and a dustbin. It uses a camera to detect obstacles and a lidar sensor to map the entire space and find where it can travel in a room with obstacles. The entire room is covered without leaving any space uncleaned, using path planning algorithms. Finally, it goes back to its charging dock on its own by retracing the path.

How does it move around?

Figure 1: Model of a vacuum robot with 2 powered wheels and a following caster wheel

The vacuum robot’s mechanical model is shown in Figure 1. It has two individually powered wheels and a caster wheel to facilitate movement. Powering the two wheels in opposite directions allows the robot to perform a turn in place. Additionally, the robot features two rotating side brushes, as seen in Figure 2, which collect dust from a wider area and direct it to the vacuum in the center.

Figure 2: Rotating side brushes to collect dust from a wider area for the vacuum pump

How can it cover the entire space efficiently?

Figure 3: Efficient path for a vacuum robot to clean a room without obstacles

1. Let's take a room without any obstacles. The efficient path to clean the room is to follow the directions shown in Figure 3. The vacuum robot follows this path and takes the 90-degree angles close to the wall using a gyroscope sensor (which can measure orientation accurately).
2. All the vertical paths here are separated by a distance to prevent overlap while cleaning, and this distance can be accurately measured and covered using a wheel encoder.
3. Thus there is no variation and the path can be repeated every single time exactly!

But what about Obstacles?

Figure 4: Efficient path in a room with obstacles using camera and lidar

1. The vacuum robot is equipped with a 2D lidar sensor to detect obstacles in the environment at a certain height, scanning the horizontal plane. As a result, it cannot detect a piece of cloth on the floor but can detect chairs, etc. This sensor gauges the distance of obstacles by emitting and collecting laser light. I wrote a newsletter explaining how lidars work if you’d like to delve deeper and gain a better understanding.
2. It uses a camera with a 3D depth sensor to recognize obstacles and detect objects like a cloth on the floor, which cannot be detected by a lidar, as we only use a 2D lidar sensor.
3. By combining the data from the lidar and camera through sensor fusion an efficient path to navigate around obstacles is generated using the path planning algorithm, as shown in Figure 4.

Does it fall off the stairs?

Figure 5: Emitting light and collecting the reflected light to detect stairs

While moving, the robot might come across stairs. To avoid potential falls, sensors are placed on the edges of the robot, where contact with stairs happens first. These sensors emit constant infrared light onto the floor, and a detector notes the reflected light. If the robot begins moving over the stair edge, the changing reflected light, caused by the growing distance between the floor and the vacuum cleaner, triggers the robot to promptly turn and prevent falling.

Fully Autonomous!

All this happens autonomously — pretty cool, right? That’s how a vacuum robot operates. Thank you for reading!

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