“…For examples, a passive walker is powered by the user-supplied forces with controlled brakes [ 8 , 9 , 10 ]. Recently, the walker powered by motors to steer the walker has attracted a lot of attention [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Patel et al [ 11 ] used an active walker as the experimental platform to exploit the interactions between an intelligent mobility aid and the human operator.…”