The drivers are driven such that they carry out a conveying displacement in {TAIL ~ the conveying direction} and {HEAD ~ a return displacement} in the opposite direction 
The drivers are driven such that they carry out a conveying displacement in { TAIL ~ the conveying direction } and { HEAD ~ a return displacement } in the opposite direction
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH