Ignore delivered files with Robocopy- Java

I have a great amount of files which I need to deliver between servers. I'm using robocopy and usually its work fine. The problem is the case when some of the files are being use by other app when copied - Robocopy compare the files stamps of the original and the copied file and failed (since the stamp of the original file is changing). How can I ignore the comparison and tell Robocopy skip the files which already been copied? Thanks!