How to move movieclip continuously and

Hi everyone

I have attached FLA file. I want to be moving this two line continuously. one line(ln1) should be coming from up. and line(ln2) should be coming from down. when both line touch to each other.both must be gone back. this all work must be continuing. the lines shound not going out that blue box.

Please help me

waiting for reply.

Thanx a lot