The control cam and a contact surface of {HEAD ~ the feeler roller} are in operative rolling contact during at least part of a period repeating in {TAIL ~ the respective periods} 
The control cam and a contact surface of { HEAD ~ the feeler roller } are in operative rolling contact during at least part of a period repeating in { TAIL ~ the respective periods }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL