US Patent 7978433 Recording-medium driving device

When a medium casing is properly inserted, a first pair of projections and a second pair of projections are passed through between a first bottom surface and a second bottom surface of a chassis in the moving direction and are thus prevented from coming into contact with the first and second bottom surfaces, thereby allowing for smooth insertion of the medium casing. In contrast, when the medium casing is inserted improperly from its wrong end, one of the projections on the lower surface of the medium casing comes into abutment with the second bottom surface of the chassis near the opening. Accordingly, an improperly inserted medium casing can be prevented from being inserted any further at an early stage of the insertion process.