Perhaps a peristaltic pump[1], with the rollers spaced appropriately to achieve the minimum incremental amount? 1: https://en.wikipedia.org/wiki/Peristaltic_pu

Perhaps a peristaltic pump[1], with the rollers spaced appropriately to achieve the minimum incremental amount? 1: https://en.wikipedia.org/wiki/Peristaltic_pump https://en.wikipedia.org/wiki/Peristaltic_pump