JPS6425005A - Dust-proof mechanism for length-measuring apparatus - Google Patents

Abstract

PURPOSE:To prevent the penetration of metal powder or the like into a reading mechanism element, by providing an elastic substance seal and a magnetic fluid seal in a gap between a post element and a frame. CONSTITUTION:A linear scale 2 is fixed in a frame 1, and a reading mechanism element is constructed of a light-emitting element 3 and a photosensing element 4 and connected to a retaining element 5 through the intermediary of the post element 10. An elastic substance seal 6 is fixed at one end to the frame 1 and seals the inside of the frame 1 from the outside with the other end made to contact slidably with the post element 10. Moreover, a permanent magnet 7 and a yoke 8 are fixed on the frame over the full length in the longitudinal direction thereof so that they are opposite to each other with the post element 10 held between, and a very small gap for sliding is provided between the yoke and the post element 10 so as to make the post element 10 slidable therethrough, while a magnetic fluid 9 is injected in the gap of the magnet 7 and the yoke 8 over the full length thereof. By forming the structure in this way, the fluid 9 is retained in the gap by its own magnetic force and a magnetic field generated by the magnet 7 and the yoke 8, so as to keep the sliding space of the post element 10 in a hermetically sealed state. Thus, the penetration of metal powder or the like is prevented by the double-seal structure of the elastic substance seal and the magnetic fluid seal.