Production of dimensionally-stable magnetic encoder employs metal carrier and co-injection molded thermoplastics of flexible and rigid-magnetic kinds locked into position for reliable operation over wide temperature range

摘要

A flexible metal strip (1) is cut and pressed to hold a first non-magnetic plastic (9). It includes holders for a succession of rigid magnetic rods (10) made of a second injected plastic material. The profiles hold and anchor the plastics. A co-injection process is employed in a mold (14) into which the strip is placed. Flexible, non-magnetic material is first injected, followed by the rigid, magnetic, isotropic or anisotropic material. The holding profile is folded against the magnetic rods after cooling and extraction, to assure retention in the flexible, part-surrounding thermoplastic body. The rods (10) are magnetized in alternation (N, S, N, S, ...). An Independent claim is included for the corresponding encoder. Preferred features: Rod holding profiles are folded tongues (6). During injection molding, magnetic properties of the plastic compound are exploited by application of a field conferring magnetic anisotropy. At least one short, powerful magnetic pulse is applied. The encoder is annular, having been so shaped before injection molding. The ends are butt-welded or seam-turned together.