During reversal the servo system which is driven into saturation senses the occurrence of {HEAD ~ zero motion} of {TAIL ~ the drive mechanism} and reverses the direction of energization of the electromagnetic drive 
During reversal the servo system which is driven into saturation senses the occurrence of { HEAD ~ zero motion } of { TAIL ~ the drive mechanism } and reverses the direction of energization of the electromagnetic drive
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH