If {TAIL ~ this embodiment} is equipped with a drive 14, the force of the drive 14 can reinforce {HEAD ~ the spring} 23 
If { TAIL ~ this embodiment } is equipped with a drive 14 , the force of the drive 14 can reinforce { HEAD ~ the spring } 23
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH