a means for comparison that compares {HEAD ~ a load detection value} obtained based upon {TAIL ~ detection signals} from said load sensors with a predetermined overload value 
obtained based upon
a means for comparison that compares { HEAD ~ a load detection value } obtained based upon { TAIL ~ detection signals } from said load sensors with a predetermined overload value
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH