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