Disc cartridge for archive data storage is made up of multi slots array and each slot keeping a disc. However, misalignment between slot and disc is caused by various disturbances sources. The archive data storage should be operated stably, able to cope with the misalignment. Because, misalignment can cause disc crash against slot walls, and miss positioning between transfer robot and disc slot. Therefore, proper detecting misalignment method should be adopted in archive data storage. In this paper, analyze allowable misalignment and propose dual sensing method based on vision system. Suggested method can simultaneously detect the upper and lower part of slots using only one detector. Each image is split by changing each optical path intentionally through lens shifting of 4f imaging system.