Directory naming

Hi, for first sorry for my english.

I need to know how to zip a folder with files and subfolders into a zip file but without the entire hierarchy name.

I mean: I would like to zip the folder "../zip/1/project_name" and I write:

$createZipFile->zipDirectory("../zip/1/project_name", "/");

I need to obtain a zip file with the only project_name folder and its files and subdirectories.

Instead I have a zip file with "../zip/1/project_name/.." etc.

If I change the output dir a new empty dir into the zip is created.

I can't understand how to use your useful class.

Thanks in advance