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