PURPOSE: To obtain extremely easily a revolution detector at a low cost and good mass productivity by forming the detector into the gear-shaped construction having hollow grooves colored to black and projecting parts colored to white.
CONSTITUTION: Plural hollow grooves 12 are formed by machining, etc. to a circular columnar bar 11 consisting of an aluminum alloy, etc. The bar 11 as an anode is electrolyzed in an electrolyte of sulfuric acid to form an alumite film having a porous layer. The bar is dipped in a dye tank contg. a black dye to color the entire circumferential surface including the grooves 12 to black. The projecting parts 13 of the bar 11 are machined off to expose the aluminum base, then the bar is anodized and is dipped in boiling pure water to hydrolyze the Al2O3 anhydride on the aluminum base surface, thereby closing the pores of the porous layer and forming the white film on the projecting parts 13. The bar 11 is cut to a prescribed size and a shaft hole 14 is formed. A shaft 10 is fixed into the hole and a revolution detector 8 is thus formed.
KIKUCHI KIMIHIRO
SATOU YOUICHI
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