The Roomba robotic vacuum uses a system with 5 IR emitters on the
docking station. Each is aimed a different direction, Center, Right,
Left, Far right, and Far left. They all transmit IR on the same carrier
wave frequency, but different data is sent to identify which one it is.
The IR detector on the Roomba is omni directional, and just detects
which beam it is in the path of. However, it can't detect the home base
from very far away and must perform a search pattern until it comes
within a few feet.
I think simpler system is just an omnidirecitonal IR emitter on the
base, then a highly directional IR sensor on the robot, perhaps by
putting the detector in a black tube (like some shrink tubing, without
shrinking). The robot spins in place until it sees the beacon, and
heads straight for it. Of course, it may not see it, and would need to
perform a search pattern and try again at another location.
It could even take one reading, then move a known distance and take
another reading to determine the change in the angle. If you know two
angles and one length, of a triangle, then this is enough information
to know the distance to the beacon. When you got closer to the beacon,
you might perform another reading to re-target it. Of course, it may
not see it, and would need to perform a search pattern and try again at
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