The elastic coupling member may be {TAIL ~ a spring member} engaging with {HEAD ~ both the driving arm} and the driven arm 
The elastic coupling member may be { TAIL ~ a spring member } engaging with { HEAD ~ both the driving arm } and the driven arm
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH