a motion device for effecting relative movement between {HEAD ~ said carriage} and {TAIL ~ a friction surface} in a first direction 
a motion device for effecting relative movement between { HEAD ~ said carriage } and { TAIL ~ a friction surface } in a first direction
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH