Are there any good non-predictive path following algorithms?

Question

All the path following steering algorithms (e.g. for robots steering to follow a colored terrain) that I can find are predictive, so they rely on the robot being able to sense some distance beyond its body. I need path following behavior on a robot with a light sensor on its underside. It can only see terrain it is directly over and so can't make any predictions; are there any standard examples of good techniques to use for this?

Answer 1

I think that the technique you are looking for will most likely depend on what environment will you be operating in as well as to what type of your resources will your robot have access to. I have used NXT robots in the past, so you might consider this video interesting (This video is not mine).

Assuming that you will be working on a flat non glossy surface, you can let your robot wander around until it finds a predefined colour. The robot can then kick in a 'path following' mechanism and will keep tracking the line. If it does not sense the line any more, it might want to try to turn right and/or left (since the line might no longer be under the robot because it has found a bend).

In this case though the robot will need in advance what is the colour of the line that it needs to follow.

Answer 2

The reason the path finding algorithms you are seeing are predictive is because the robot needs to be able to interpret what it is "seeing" in context.

For instance, consider a coloured path in the form of a straight line. Even in this simple example, how is the robot to know:

• Whether there is a coloured square in front of it, hence it should advance
• Which direction it is even travelling in.

These two questions are the fundamental goals the algorithm you are looking for would answer (and things would get more complex as you add more difficult terrain and paths).

The first can only be answered with suitable forward-looking ability (hence a predictive algorithm), and the latter can only be answered with some memory of the previous state.

Based solely on the details you provided in your question, you wouldn't be able to implement an appropriate solution. Although, I would imagine that your sensor input and on-board memory would in fact be suitable for a predictive solution, you may just need to investigate further what the capabilities of your hardware allow for.