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