a control means including {HEAD ~ a CPU} for controlling {TAIL ~ said wheel driving means} in accordance with the outputs of said sensor means 
for controlling
a control means including { HEAD ~ a CPU } for controlling { TAIL ~ said wheel driving means } in accordance with the outputs of said sensor means
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH