| 摘要 |
PURPOSE:To facilitate the formation of detection parts and nondetection parts as an encoder plate by heating an electret film which is polarized electrically as a whole at specific intervals and thus forming unpolarized areas, and forming detection parts and nondetection parts on the encoder plate. CONSTITUTION:A thermal head 2 is arranged on a long-sized beltlike film 1 of polyvinylidene fluoride (PVDF) which is polarized electrically as a whole, and the film 1 is heated selectively to form unpolarized areas 3b successively. Said film 1 is stuck on the outer peripheral surface of a metallic rotary disk 5 which rotates together with a metallic shaft 4, and a metallic fixed plate 6 is arranged opposite to the outer peripheral surface of the rotary disk 5 across a fine gap. Then, the polarized areas 3a and unpolarized areas 3b are moved to detect a fine voltage alternately between the rotary disk 5 and fixed disk 6.
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