Hi,
I am working on a project, i.e following of a person by a robot.
I am not an expert although know enough to start with.
Please give me suggestions about the sensors so that i could use , which will help the robot to follow the person, also with suggestions please tell me a little how to use them.
NOTE: the robot should follow the specific person only if there are others.
PLEASE HELP!!
THANKs
As Andy said, something like a quad encoder could control the vector.
If you're thinking of fairly short distances something like the antenna-on-chip XBee's are great in a low-power small package. I'd likely make the vector sensing a two-part system:
1. Linked XBee's to let the robot know that it's paired device wants to be followed. You could also use Bluetooth Low-Energy, I suppose. I just prefer XBee, as you can get them in a 900MHz frequency band to avoid all the noise on the 2.4GHz ISM band.
2. Ultrasound distance sensors to keep the robot at whatever distance you define from the person, but linked. If the signal was blocked or became out of range you could code for some type of watchdog on the master to let the person know there was a problem.
I know others prefer to use signal timing on a radio beam to let the slave know a vector. That's an option also. I'd put the onus on the user to be responsible for obstacle avoidance, and negotiating things like escalators. On the other hand, if you like calculating Eigenvalues for autonomous robots, you could go that route. 
It partly depends upon what type of control (and controller) you want to use. If you want something that simply follows a master that's far less work than having a completely autonomous system.
