ultrasound based traking

i have this major project(about which i have been talkin about in many posts) which requires us to make a device that will track an object. it has an ultrasound and IR sensors and servos to move it around.

i get the principle of detecting the device. basically you get the servo to move from position to position until it detects a device within its range. but when i does, how do you then track the device and make sure the sensor is always with it?or even after detection is it jus a case of doing more rapid scanning?

Are you tracking a passive object, or another device? It could be done relatively sophisticatedly with good control of the ultrasound device and a pair of receviers you can use the phase difference to determine direction. Or scanning with the IR sensors. It really depends on how your sensors are interfaced and how much control you have over them, also exactly what you're tracking.

we'll be tracking a passive object. basically something like a polystyrene ball, or someone's hand or a book..

so is it possible to use phase differences and intelligent interfacing between the sensors to track a passive object effectively?

You'd have to send out a very short pulse of a it's resonant frequency and then immediatly listen for the return and measure the time different between the two microphones. Pretty precise timing is needed, and avoiding confusion from echo's is difficult (which is why you have to use a short pulse)
It depends on exactly what you have to work with.

IR sensing can be much simpler but not as precise. Basically you design optics so it has a very narrow angle of view and then spin the IR Sensor, preferably with IR illumination. Anything that glows from the ir light will provide a strong return signal on the IR sensor, but it's subject to ambient light conditions and the IR reflectivity of the object you're looking at and the rest of the enironment. You would basically spin the IR transmitter/receiver in a 360 degree circle and look for sharp peaks in the IR sensor output, that would corespond with the edges of an object that reflected IR light. Pretty simple in theory, but coding an actual effective routine that does it is a different story.

I hope that helps a bit.