I think that you are on the right track.
Decide on the Key field format of the Bin. For example it might be the result of a calculated field on the child table with this formula
List("-",ToText([date]), [type], [class], [courier])
You can make the Key field of the Bins table be a text string that will be the 4 fields concatenated together like the formula does, but for now we will keep it simple and it will just be a text field.
Make a field on the parent table which will always calculate to true (checked), so the formula for [Bin exists?] would be
true
and look that up down to the Batches table. So now the Batch record knows if it needed to trigger the creation of a parent Bin.
Then set up an Action to fire when the Batch is added or modified and the lookup of the [Bin Exists?] is false to create the Bin record and populate its key field with the value of the calculated key field.
