Patent ID: 8658965

Claim:
An encoder comprising: a light-emitting unit which emits light; a moving part which moves relative to the light-emitting unit; a first pattern track which comprises a plurality of first unit patterns sequentially formed on the moving part, separated from one another and having different widths; a first light-receiving unit which is disposed to correspond to the light-emitting unit, and detects first information about light received from the light-emitting unit via a first pattern of the first unit patterns; at least one second light-receiving unit which is disposed to correspond to the light-emitting unit, and detects second information about light received from the light-emitting unit via at least one second pattern of the first unit patterns; and a displacement calculating unit which calculates a relative displacement of the moving part with respect to a reference position based on the first and second information, wherein the first light-receiving unit detects a width of the first pattern, in a direction parallel to a moving direction of the moving part, based on the first information, and the at least one second light-receiving unit detects each width of the at least one second pattern, in the direction, based on the second information, wherein the displacement calculating unit calculates the relative displacement based on the width of the first pattern and the each width of the at least one second pattern, and wherein the displacement calculating unit calculates the width of the first pattern and the each width of the at least one second pattern based on a speed of the moving part, a pulse width of the light received from the light-emitting unit via the first pattern and each pulse width of the light received from the light-emitting unit via the at least one second pattern.