Abstract: A rotary disc for an optical rotary encoder has a diameter of 15 to 50 mm, a thickness of 20 to 200 .mu.m and 200 to 1,500 slits. The disc is made of nickel phosphorous alloy. A warpage of the disc is not greater than 100 .mu.m. Such a rotary disc is produced in accordance with a method comprising the steps of holding the disc between two planes and applying heat and pressure to the clamped disc. It is desirable to use plating of metal onto the disc in a pattern.

Abstract: A printed coil unit for use in a very thin type flat brushless motor or a linear actuator, in which a magnetic sensor element having a thickness smaller than 0.6 mm is embedded integrally within the coil unit without projecting therefrom in a region located outside and in the vicinity of spiral conductor coil patterns. The printed coil unit includes a single printed coil sheet or a lamination of such coil sheets each having more than one spiral conductor patterns on the same plane. A magnetic sensor element, such as Hall element or magneto-resistance element having a thickness equal to or smaller than that of the printed coil sheet is embedded within the coil sheet at blank regions located between adjacent spiral conductor patterns, or regions made availably by diminishing the size of a selected one of the spiral conductor patterns. A moving speed detecting coil or patterned conductor can be additionally provided on the other available area of the coil sheet.