In another alternative, the means for controlling the timing of the first and second actuators is further operable to repeatedly reverse {HEAD ~ a direction} of translation of the movable member of each actuator relative to {TAIL ~ the base member} at substantially the same time 
In another alternative , the means for controlling the timing of the first and second actuators is further operable to repeatedly reverse { HEAD ~ a direction } of translation of the movable member of each actuator relative to { TAIL ~ the base member } at substantially the same time
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH