[jQuery] jQuery Form Plugin, and ajax submit without submit button

[Giovanni Battista Lenoci]

Hi, I'm using this fantastic plugin but if I try to submit the form
using

$('#form_id')[0].submit() the ajaxform it's not fired, it behaves like
it's a normal form, and I'm redirected to the ajax page.

What I want to do is to submit the form when I check a checkbox.

Can you help me?

thank you