Patent ID: 8422025

Claim:
An optical encoder comprising: a light source; a scale disposed so as to face the light source; a light receiving element configured to receive luminous flux from the light source through the scale; and a signal processing circuit configured to process an output signal of the light receiving element, wherein a light emitting window of the light source is constituted of a collection of a plurality of point light sources and has a shape which meets the following expression: 0 ≤ ∫ S ⁢ ∫ Po ⁡ ( x ⁢ ⁢ 1 , y ⁢ ⁢ 1 ) · Cos ⁡ ( Π × N × ( x ⁢ ⁢ 2 - x ⁢ ⁢ 1 ) / p ) ⁢ ⅆ y ⁢ ⁢ 1 ⁢ ⁢ ⅆ x ⁢ ⁢ 1 ∫ S ⁢ ∫ Po ⁡ ( x ⁢ ⁢ 1 , y ⁢ ⁢ 1 ) · Cos ⁡ ( Π × ( x ⁢ ⁢ 2 - x ⁢ ⁢ 1 ) / p ) ⁢ ⅆ y ⁢ ⁢ 1 ⁢ ⁢ ⅆ x ⁢ ⁢ 1 ≤ 0.02 where S is an entire region in the light emitting window that is an integration range, Po(x1, y1) is a function representing a light intensity distribution in a near field at an XY coordinate (x1, y1) of the light emitting window, p is a grating pitch of the scale, N is a specific order of a harmonic component (N: 1, 2, 3, . . . ), and x2 is an axis in a displacement detecting direction on a surface of the light receiving element.