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Ultrasonic sensor exposure problem

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The application of ultrasonic sensors is simple in principle, convenient, and low in cost. However, current ultrasonic sensors have some shortcomings, such as reflection problems, noise, and crossover problems.



1. Reflection problem


If the detected object is always at the right angle, the ultrasonic sensor will get the right angle. Unfortunately, in actual use, few detected objects can be detected correctly.


There may be several errors:


2. Triangular error


When the measured object is at a certain angle with the sensor, there is a triangle error between the detected distance and the actual distance.


3. Mirror reflection


This problem is the same as the reflection of light learned in high school physics. At a certain angle, the sound waves emitted are reflected off the smooth surface of the object, so no echoes can be generated, and distance readings cannot be generated. At this time, the ultrasonic sensor will ignore the existence of this object.


4. Multiple reflections


This phenomenon is more common when detecting wall corners or objects with similar structures. The sound wave is received by the sensor after many bounces, so the actual detection value is not the true distance value.


These problems can be solved by using multiple ultrasonic rings arranged at a certain angle. By detecting the return value of multiple ultrasonic waves, it is used to filter out the correct readings.


5. Noise


Although the working frequency of most ultrasonic sensors is 40-45Khz, it is much higher than the frequency that humans can hear. But the surrounding environment will also produce noise of similar frequency. For example, the motor will generate a certain high frequency during the rotation, the high frequency noise generated by the friction of the wheel on the hard ground, the jitter of the robot itself, and even when there are multiple robots, the sound waves emitted by the ultrasonic sensors of other robots , These will cause the sensor to receive the wrong signal.


This problem can be solved by encoding the transmitted ultrasonic waves, such as transmitting a set of sound waves of different lengths, and only when the probe detects the same combination of sound waves, the distance calculation is performed. This can effectively avoid misreading caused by environmental noise.


6. Cross-problems


The crossover problem is caused when multiple ultrasonic sensors are installed on the robot at a certain angle. The sound wave emitted by the ultrasonic X is reflected by the mirror surface and is obtained by the sensors Z and Y. At this time, Z and Y will calculate the distance value based on this signal, so that the correct measurement cannot be obtained.


The solution can be by encoding the signal sent by each sensor. Let each ultrasonic sensor only listen to its own voice.