For check-in, you can use following API in expression robot itself. For you, object is EPMDoc and note is checkin comments.
wt.vc.wip.WorkInProgressHelper.service.checkin(Workable object, String note)
Side Note: If its a brand new EPMDocument, you might want to persist it. For you, obj is EPMDoc.
wt.fc.PersistenceHelper.manager.save(Persistable obj);