A displacement of the laser beam spot outputted from {HEAD ~ 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 
A displacement of the laser beam spot outputted from { HEAD ~ 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
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH