control means for controlling the speed of {HEAD ~ the electric motor} to thereby control {TAIL ~ the rotating speed} of the tubular member 
to control
control means for controlling the speed of { HEAD ~ the electric motor } to thereby control { TAIL ~ the rotating speed } of the tubular member
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH