I am using Share point 2010.

I have a list. Multiple attachments are added to an item at different times. The attachments are stored in a separate document library. An workflow copies all the attachments to the attachment document library.  As the attachments are added at different times I have set the workflow to start when the item is modified, but this means every time the item is updated and saved all the attachments are copied to the attachment library which means existing attachments already copied are copied again.

I need a workflow that is triggered when the item is modified and checks if the attachment is already listed in the attachment library. If it is then do nothing if it isn't copy to the attachment library.

The only way I found is to use the overwrite option on the copy action that adds for any new name that already exists the current date and time at the end of the name  ie Name (02-08-2018_16-34-40). Then on the attachment document library I have a workflow to delete items where the name includes a bracket (. 

This is no ideal and I wonder if there is a better way.

I was thinking of using the setting condition but I can't see how I can reference the attachment name in the list.

Any ideas, suggestions?