RP6 ROBOT SYSTEM - 2. The RP6 in detail
brightest spot in the room! For example if you illuminate the floor with a very bright
halogen-torch, the robot will follow the bright light spot on the floor.
Of course you may try the opposite: the robot could be programmed to hide from
bright light sources.
You can refine this by mounting one or two additional LDRs at the backside of the ro-
bot. By using only the two sensors which robot has by default, it can not distinguish
between bright light in the front and in the back too well. Two of the A/D-converter
channels are still free...
2.3.3. Anti Collision System (ACS)
From the software's point of view, the most complex Sensor is the
ACS – the “Anti Collision System”! The ACS consists of an integrated
infrared (IR)-receiver circuit (see fig.) and two IR LEDs, located at
the left and right front-side of the sensor PCB. The Microcontroller is
controlling the IR-LEDs directly. The controlling functions can be
changed and improved by yourself if necessary! The predecessor
model had a special controller for this purpose and the user could not
modify the software of this device.
The IR LEDs are transmitting short infrared pulses modulated with
36kHz, which can be detected by the IR-receiver. Whenever IR-pulses
are reflected by an object and received back by the IR-receiver, the microcontroller
may react to the situation and start an escape manoeuvre. In order to avoid too much
sensitivity, the ACS routines will delay detection events until the system has received
a predefined number of pulses within a small period of time. Additionally, the ACS
synchronizes the detection with the RC5-receiver routines and will not react on RC5-
signals from TV/Hifi remote controls. Other codes however may interfere with the ACS
and the robot may try to avoid non-existent obstacles!
Given that the ACS has one IR LED aligned to the left and one to the right, it can
roughly determine whether the obstacle is in the middle, left or right.
The system allows you to change the pulsed intensity of both IR LEDs at three levels.
But even at the highest current level, the ACS may not detect all obstacles reliably.
This is greatly dependant on surface reflectivity of the obstacles!
Of course a black object will reflect less IR-light compared to a white obstacle and a
reflecting square-edged object may lead the IR-light mainly into a few special direc-
tions. Therefore the ACS range is drastically depend on obstacle-surface! This depend-
ency must be considered as a basic drawback of all IR-sensor systems (at least in this
price-class).
However the robot can detect and avoid most obstacles flawlessly. If ACS-detection
fails, there are still the bumpers with touch sensor elements. And if the touch sensors
fails the robot may detect motor blocking by its current sensors or encoders!
If you are not satisfied with these sensor systems, you might consider mounting some
ultrasonic sensors for example.
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