If you are a leek grower who produces tons of leeks throughout the season, you will already have a production line that may, or may not be automated.
If you are selling leeks with their roots removed, presentation and quality of cut is important. Worst case scenario is that your conveyor is feeding a small army of people armed with knives who pick up a leek and trim it at the base of the stem to remove the roots. The key is to cut the stem at exactly the right place; leaving some roots on is unacceptable, cutting too much into the stem damages the shelf life of the leek as it will dry out and start to ‘telescope’. This affects the shelf life and therefore the value of your product.
You may have a fully automated leek trimming line, in which case it is highly likely that this is without any ‘intelligence’ in which case there will be a mechanical assembly that pushes the leek up to an end stop so that the cut can be estimated. This means that some leeks will be undercut and some will be overcut.