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