A vision system examines droplets monitoring quality and {HEAD ~ a feedback signal} to vary the material in {TAIL ~ each droplet} 
A vision system examines droplets monitoring quality and { HEAD ~ a feedback signal } to vary the material in { TAIL ~ each droplet }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL