Tom,
If you're asking in relation to NetBackup (not in relation to the library itself), then here goes:
In Media and Device Management, expand the Media section
Next expand the Robots section
Right-Click on the ACS(0) item and select 'Inventory Robot'
Make sure you select 'Update volume configuration' under 'Inventory operation'
You can also check the 'Empty media access port prior to update' to scan for any tapes input.
Hope that's what you were asking for.