Realization of recharging method of sweeping robot
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Realization of recharging method of sweeping robot
Summary
The recharging methods of sweeping robots currently on the market can be roughly divided into the following types according to the different sensors used: infrared sensors, ultrasonic sensors, vision sensors, laser sensors , and the method of mixing the above-mentioned sensors .
In the work of the sweeping robot, when it detects that the battery is insufficient, it will automatically look for the charging stand. Due to the limitations of various sensors, we need to maximize the strengths and avoid weaknesses to give full play to the advantages of various sensors. Therefore, in this process, it can be divided into long-distance recharging and short- distance recharging according to the distance from the charging base :
in the long-distance recharging method: a relatively high-end sweeping robot will add a path planning algorithm, which is constructed by the equipped laser sensor Take out the map of the room and mark the location of the charging stand at the same time. When charging is needed, it automatically plans a path back to the place near the charging base. The low-end ones use the method of walking along the wall to find the charging stand. In fact, most of our sweeping robots use the latter method to return to the place near the charging stand.
In the short-distance recharging method: generally install an infrared sensor or an ultrasonic sensor on the charging base, and coordinate with the sensor on the body of the sweeping robot to complete the positioning. 70% of sweeping robots on the market use separate infrared sensors and other sensor fusion methods, while some use ultrasonic sensors.
Recharge method based on infrared sensor
For the use of a single infrared sensor, take Samsung's VR9000 as an example: 
the three sets of infrared transmitters of the charging base all emit infrared modulation coded signals, and the sweeping robot is equipped with multiple infrared receiving devices in front of it. It is used to detect the intensity of the infrared signal and realize the docking through a certain algorithm. The disadvantage of this method is that the intensity of the infrared signal is affected by many factors, so the recharging speed is slow, the total path is longer, and the accuracy is not very high. Therefore, a multi-sensor fusion method is proposed. Some sweeping robots have added cameras and laser transmitters to infrared sensors. 
On the basis of a single infrared sensor, the laser's high brightness and high unidirectional characteristics are used as an accurate direction signal. Install the laser transmitter on the charging base, and the linear laser emitted will be projected on the ground to form a high-brightness straight line. At the same time, the camera on the sweeping robot is used to shoot and identify the laser line projected on the ground. Calculate the slope and position of the laser line to calculate the angle and distance that the robot deviates from the laser line, so as to guide the robot to the central axis of the charging base, and then gradually complete the docking with the charging base.
Lidar-based recharge method
We know that there is a 360-degree rotating laser rangefinder on the sweeping robot, which is often used to build maps and avoid obstacles. Many domestic robots use this sensor to perform a special treatment on the charging stand, which is equivalent to attaching a label. Generally, the surface of the charging seat of the cleaning robot is divided into uneven areas with different heights. The material of the concave area has high light reflectivity, and the material of the convex area has high light absorption rate. Lidar recharges by identifying this special area.
Recharge method based on ultrasonic radar
Two ultrasonic radar receivers are installed at both ends of the charging base, and the transmitter is installed on the sweeping robot. When recharging is required, the relevant ultrasonic transmitter on the sweeping robot emits ultrasonic waves, and the ultrasonic waves on the charging stand receive the ultrasonic waves and then proceed. deal with. Obtain the position and posture of the robot relative to the charging base, and then feedback the position information to the robot, so that the robot can continuously adjust the position and posture. Shown in the picture is the charging base of a Proscenic smart sweeper:
Comparison of the above methods
| method | advantage | Disadvantage |
|---|---|---|
| Single infrared sensor | Low cost, wide range, easy to develop | Poor accuracy, greater environmental impact, and low recharging efficiency |
| Infrared camera fusion | Higher accuracy, which improves the efficiency of recharging | Development is difficult and requires hardware support with good computing power, which increases the cost |
| Lidar sensor | Wide detection range, relatively stable | The development is more complicated and requires better hardware system and algorithm support |
| Ultrasonic radar | Can measure the specific distance value, relatively accurate, low cost, easy to develop | The directionality is poor, and it is easily affected by the environment (temperature, humidity, obstacles, etc.) |
Reference materials:
[1] Wei Yin. Design and implementation of automatic recharging system for sweeping robots[D]. University of Science and Technology of China, 2018.