{HEAD ~ A displacement} of the laser beam spot outputted from {TAIL ~ the actuator} is differentiated by a differentiator and converted to a signal corresponding to the velocity of the movement of the laser beam spot 
outputted from
{ HEAD ~ A displacement } of the laser beam spot outputted from { TAIL ~ the actuator } is differentiated by a differentiator and converted to a signal corresponding to the velocity of the movement of the laser beam spot
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH