Patent ID: 8829421

Claim:
An optical encoder comprising: an optical scale having periodical optical patterns and can be relatively and angularly displaced; a projector for irradiating the optical scale with light; a light receiver for receiving light from the optical scale; and a calculator for calculating an absolute rotation angle θ of the optical scale in accordance with a signal from the light receiver; wherein the optical patterns include a plurality of light shielding portions and a plurality of light transmitting portions, each of the portions being located alternately, and when a pitch of an n-th light shielding portion in a predetermined circumferential direction is denoted by Pn and a width of the n-th light shielding portion is denoted by Wn, a transmissivity T(θn) corresponding to an angle θn of the n-th light shielding portion and the pitch Pn of the light shielding portion satisfy the following equations (A1 and (A2), and the width Wn of the light shielding portion in the optical patterns is expressed by the following equation (A3) including a pitch PH of the light shielding portion, a constant A and a coefficient m (m is a real number larger than zero) [ Equation ⁢ ⁢ 1 ] T ⁡ ( θ n ) = P n - W n P n = 1 - W n P n ( A1 ) θ n = θ n + 1 + P n ( A2 ) ( Wn ′ ) m = A Pn . ( A3 )