I am building a robot that will follow a target as the target moves around. I would like some help with the setup for tracking the target. The most obvious solutions are Ultrasound or Infrared sensors, but for this application, they won't work. Imagine that the robot is placed into a crowded area and asked to move towards a particular person in the area (for the sake of simplicity, assume the person is less than 5 meters away). Is there some kind of radar or radio solution to this, or anything?
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$\begingroup$ We really need a bit more information to answer this properly. Solutions to robotics problems are heavily dependent on the environment and what you are trying to achieve. Information like what type of robot (does it fly, is it land based at eye level, ankle level?) would help. How do you acquire the target (a controller manually selects the target, rule based classification, can the target be physically tagged with something, etc). $\endgroup$– AmochMay 23, 2013 at 1:32
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$\begingroup$ Right away, I am thinking of an RF solution where the person to be followed has an emitter. The robot could have a couple of tuned detectors mounted to scanning servos to help determine which direction the signal is coming from, following it based on signal strength, but this could have a lot of complications. I agree with @anorton - this should be migrated to Robotics.SE to get a good answer; it's not the best fit here. $\endgroup$– Kurt E. ClothierMay 23, 2013 at 2:27
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$\begingroup$ @KurtEClothier "I am thinking of an RF solution where the person to be followed has an emitter" Right, so clearly, we need to build an ... emitter follower. $\endgroup$– KazMay 23, 2013 at 15:19
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2 Answers
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In a broad sense, there are a couple of ways to do this, but they basically boil down to the problem of how do you know what person you're going towards?
If it's feasible to give the person a flashlight or some light source (IR or visible), you could use light sensitive elements to determine where to go.
Magnetic fields could also be used, by giving the person in question a strong enough magnet. (But it would have to be pretty strong, so I don't think this is as feasible...)
A final resort would be to attempt some form of a vision system. For instance, if you gave the person a lime-green ball, a vision system could pick up on that, and treat it as a target.
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$\begingroup$ Ideally, the person being followed could carry something like a transmitter to have the robot follow them. It would NOT be ideal for that person to be followed with a vision based approach, because I would not want the robot to be distracted if, for example, someone walked between it and the target. Magnets are no good, because of their propensity to destroy sensitive electronics. $\endgroup$– RJacksonMay 23, 2013 at 2:48
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4$\begingroup$ It's a rather large misconception that magnets destroy sensitive electronics. At most, you'll get interference, and that's in rare cases. In fact, most modern electronics aren't affected by magnetic fields of reasonable strength, with the exception of spinning hard disks. $\endgroup$– Radrider33May 23, 2013 at 4:38
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The tricky part with what you want to do is that matching a person to some electronic representation of their "signature" is a very difficult task to do. Outside of some advanced facial recognition software, or tweaked vision software that could recognize a lime green shirt for example, there isn't much you can do.
I thought of something I haven't seen suggested elsewhere so I don't know if something like this exists or not but it seems like it could work for you with development. Perhaps using an thermal infrared camera to calibrate a thermal image of you putting in your height dimensions would work. Ultimately you are still getting into a vision based solution but a thermal camera would auto-greenscreen your whole body so to speak so you wouldn't have to worry about wearing the right color clothes or vibrantly colored clothes. It also wouldn't matter which direction you were facing. One caveat would be if you sat down or bent over, you wouldn't be properly height matched so something would have to account for that.
Anyways, just thought I'd throw that idea out there. It wouldn't work in a crowded area as well as you being the only one wearing vibrant green and color matching with a vision solution. Perhaps a combination of the two? Two cameras are better than one.
The issue with any kind of field based approach is that the robot wouldn't know in which direction it was coming from without enough resolution which might force one to get expensive high resolution equipment. Also, the smaller the robot, the more expensive and higher res equipment one would need to triangulate a point of origin.
Alternatively, sound signatures could work. Sound waves are slower than electromagnetic waves and so would be easier to triangulate. You could also use a frequency that humans/animals cannot hear. You wouldn't need very high end equipment I don't think if you orient mics at appropriately far angles apart. Imagine a "follow my voice" kind of scenario.
Perhaps RF would work here too as mentioned but it does depend on the size/equipment.
