Infra-red sensors calibration

We are using distance sensors in order to inform the operator that the mobile base is going to encounter a staircase step or a ditch. They measure the length between the mobile base and the nearest obstacle. We use six distance sensors. One in front and one behind to inform if there is an obstacle in the path or not and four sensors to inform if the mobile base is near a hole.

We decided to use the same distance sensors that we used during the Pusing Robots project since we already knew how to use them. On top of that, they are easy to program and they are compatible with Arduino. It is the Pololu Carrier with Sharp GP2Y0A60SZLF Analog Distance Sensor 10-150cm 5V.

Once we received all of our sensors, we had to calibrate them in order to use them as we would like. To do that, we made a little calibration bench. On a breadboard, we connected all the sensors to the Arduino and all the sensors side to side, facing the same direction. With every sensor, we measured the sensor value received from 10 to 50 cm every 2 cm. This is the range of distance that interests us and it doesn't have to be too precise. A precision of +/- 3 cm is enough. When this part was done, we injected all the data on an Excel, drew the graph of the sensor value for each distance and finally we drew the trend line. The trend line gives us the fonction to use in order to translate the sensor value in a distance in centimeters. The trend line is a power function and each of the trend line had a R² = 0,99.

To verify that the sensors are correctly calibrated, we then used them all together to measure the same length and to verify that there is little difference between the different measures. The highest difference measure was 2cm between the min measure and the max measure which is very good for the precision we need.