The current is automatically reversed at the point of {HEAD ~ zero motion} of {TAIL ~ the reciprocating mechanism} during each rebound 
of
The current is automatically reversed at the point of { HEAD ~ zero motion } of { TAIL ~ the reciprocating mechanism } during each rebound
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