{HEAD ~ The arms} 13,14 maintain {TAIL ~ their inward positions}, as shown in FIG 2b, during the movement thereby preventing stacks falling during the motion 
maintain
{ HEAD ~ The arms } 13,14 maintain { TAIL ~ their inward positions } , as shown in FIG 2b , during the movement thereby preventing stacks falling during the motion
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH