[Problems to be Solved] To provide a rotary encoder capable of carrying out self-calibration for a horizontal encoder as well as a vertical encoder without requiring special equipment and simply and inexpensively with a high degree of accuracy while reducing the burden on a worker. [Means for Solving the Problems] In a rotary encoder including: a rotary disk ( 1 ) with an angle code ( 11 ); a light source that irradiates the angle code; a CCD linear sensor ( 3 ) that reads the angle code; and a processing unit that acquires a reading value f(θ) based on the angle code read by the CCD linear sensor, every time the rotary disk is rotated by a predetermined angle, where a rotation angle of the rotary disk is provided as θ and an angle from the rotation angle θ is provided as φ, based on a change in a difference g(θ,φ) between reading values f(θ+φ) and f(θ) within a reading range on the CCD linear sensor, the difference g(θ,φ) is determined as a Fourier series, and self-calibration of the reading value f(θ) of 0 to 360° is carried out based on the result.
1. A rotary encoder comprising: a rotary disk with an angle code; a light source that irradiates the angle code; a detector that reads the angle code; and a processing unit that acquires a reading value f(θ) based on the angle code read by the detector, wherein
every time the rotary disk is rotated by a predetermined angle, where a rotation angle of the rotary disk is provided as θ and an arbitrary angle from the rotation angle θ within a reading range on the detector is provided as φ, the processing unit acquires reading values f(θ+φ) and f(θ) within the reading range on the detector, and self-calibrates the reading value f(θ) based on a change in a difference g(θ,φ) between the reading values f(θ+φ) and f(θ) when the rotary disk is rotated one turn.
2. The rotary encoder according to claim 1 , wherein the rotational position of the rotary disk where the reading values f(θ+φ) and f(θ) are acquired is provided as a position where 360° is roughly equally divided and a position where the reading range on the detector is overlapped at an adjacent rotational position thereto, an average g m (φ) of the differences g(θ,φ) between the reading values f(θ+φ) and f(θ) traversing one turn and deviations h(θ,φ) between the differences g(θ,φ)and the average g m (φ) at respective rotational positions are taken, and by arranging while overlapping the deviations h(θ,φ) in parts where the reading ranges are overlapped between adjacent rotation angle positions, self-calibration of the reading value f(θ) of 0 to 360° is carried out.
3. The rotary encoder according to claim 1 , wherein the rotational position of the rotary disk where the reading values f(θ+φ) and f(θ) are acquired is provided as a position where 360° is roughly equally divided, based on a change in the difference g(θ,φ) between the reading values f(θ+φ) and f(θ), the difference g(θ,φ) is determined as a Fourier series, and self-calibration of the reading value f(θ) of 0 to 360° is carried out based on the result.
4. The rotary encoder according to claim 3 , wherein in the Fourier series, one or more arbitrary higher harmonics are determined.
5. The rotary encoder according to claim 1 , wherein for the arbitrary angle φ, one or more arbitrary positions are used.
6. The rotary encoder according to claim 1 , wherein the reading values f(θ+φ) and f(θ) are acquired by averaging a large number of times of reading values.