creating a self parking (only parallel)

[philo314]

I'm now trying to program a self parking car based on labview. I tried to use ultrasonic sensor to measure the distance of the broadside and use the rotation of the motor to control the distance of the car's moving. But there's always a problem that the distance of the ultrasonic sensor often equals 0. How could I deal with it? Or maybe there's a better method to realize self-parking

[Chris_Garratt_NIUK]

Hi Philo314,

If you're ultrasonic sensors then you are likely to see saturation at close distances which will result in a distance of zero. When choosing sensors, it is important to check their 'near field effect', which is the distance under which the data returned cannot be trusted.

What sensors are you using?

Best Regards,

Chris

[pjr1121]

I don't know how much control you have of the sensors themselves but you may also need to consider ringing of the sensor mount.  As the ultrasonic pulse is emitted, the sensor mount vibrates for a short time.  If you try detecting a pulse during this same time period, you will get a false reading.  Lets say you are trying to detect something 6 inches away, the ultrasonic pulse reflects back to the sensor in about 20 ms, which may be too fast for your particular sensor.  To avoid this, many commercial systems use a group of sensors and alternate which sensors emit and which detect.  The second sensor also increases the distance for the pulse to travel, reducing the time requirements of your system.

Very well designed ultrasonic sensors can indeed work by themselves at short distances but you need to be certain.