Patent ID: 7365654
Filing Date: 2008-04-29
Classification: G01D

Abstract:
1. An absolute angle detection apparatus comprising: a first rotating disc retained by a rotating body; a first code pattern line and a second code pattern line provided along different circumferences on the first rotating disc; a first detection element group including a plurality of detection elements arranged so as to face the first code pattern line; a second detection element group including a plurality of detection elements arranged so as to face the second code pattern line; and a plurality of sectors assigned to the first rotating disc, each sector corresponding to an angle obtained by dividing 360° by an even number, wherein each of the sectors has combinations of first code lines and second code lines, each first code line including a set of code elements supplied from the first detection element group and each second code line including a set of code elements supplied from the second detection element group, wherein the first code lines are Gray codes including third code lines that do not appear the same even when a digit from which the third code lines are read is changed and fourth code lines that appear the same when a digit from which the fourth code lines are read is changed, wherein the first code lines at adjacent steps differ from each other at one bit and the first code lines at the first and last steps in each sector differ from each other at one bit, wherein, in each sector, each of the first code lines is shifted by one digit in a predetermined direction at every predetermined number of steps and the first code line corresponding to the maximum shift becomes identical to the first code line without shift when the first code line corresponding to the maximum shift is further shifted by one digit in the predetermined direction, and wherein the second code lines identify the fourth code lines.