🚀 go-pugleaf

Have you considered using sonics?  It shouldn't be that hard to broadcast
a narrow beam of sound and wait for the echo.  If the speaker-mike is on
a rotating boom, you can tell what angle (relative the the robot) the object
is at.  It may even be possible to determine the size of the object based on
the volume of the echo (with the delay giving the range).

I seem to recall that there are surveying instruments on the market that you
simply point at a target and they digitally read out the range.  One of these
could be connected to a hardware interface fairly easily as well (I think).

I'm not a robotics person, so forgive me if this idea is way out in left
field.
--
     __
    /..\      In quest of knowledge....
 --mm--mm--         Mike Gobbi