This sensor device allows two measures:
- The normal ambient light. This measure is made using only the re-
ceiver part of the device, without emitting light with the emitter. A
new measurement is made every 33 ms. During the 33 ms, the eleven
sensors are read in a sequential way every 3 ms. The value returned
at a given time is the result of the last measurement made.
- The light reflected by obstacles (= proximity). This measure is made
emitting light using the emitter part of the device. The returned
value is the difference between the measurement made emitting light
and the light measured without light emission (ambient light). A new
measurement is made every 33 ms. During the 33 ms, the eleven
sensors are read in a sequential way every 3 ms. The value returned
at a given time is the result of the last measurement made.
The output of each measurement is an analog value converted to a 12
bit digital value . The following two sections illustrate the meaning of this
12 bit values.
3.3.1
Ambient light measurements
Ambient light measurement is strongly influenced by the robot’s environ-
ment. Depending on the light source type, color, and distance, ambient
light measurement profile might vary.
It is not recommended to use
light source with large emission in the infrared range, as this could
confuse the IR sensors.
3.3.2
Reflected light measurements (proximity)
Sensors are mainly meant to detect obstacles around the Khepera. Mea-
surements for reflected light depends on objects reflectivity and on ambient
light conditions. Objects color, materials and surfaces do have an influence
on the sensors response. Moreover, as any sensor, IR sensors are subject
to environmental noise. For all these reasons, graphics below are given for
information only and should not be considered as references.
Khepera III manual ver 2.2
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