Hello, Inchoateknowledge. Thank you very much for your reply.
So, you're saying that if you expect the hearer to say "no", you should ask, "Will you not join us?" , not "Won't you join us?" and if you expect him to say "yes", then you should ask, "Will you join us?", aren't you?
If somebody has a different opinion, please tell me.
Well, yes, I have a different opinion, although what Inchoate could also be correct, depending on context. To me, they are largely interchangeable, but the "will you" can have a sense of genuine inquiry ("Are you coming or not?") while the "won't you" has a sense of "I really hope you are coming."
If you have ALREADY invited the person, and have gotten the impression that he's not coming,