GSI Lumonics Inc. of Billerica, Mass., has signed a definitive agreement under which it will purchase all shares of MicroE Systems Corp. for $55 million in cash. The Natick, Mass., company designs and manufactures position encoders for precision motion control applications in the medical, electronics, data storage, semiconductor and industrial automation markets. Its products and technology are expected to complement GSI Lumonics' portfolio of enabling precision motion components and subsystems.