Rotary encoder, rotary encoder system, and rotation angle detection method using rotary encoder

A rotary encoder system comprising:

• a rotary encoder including:
• a rotary scale connected to a rotating shaft of a rotating body as a detection target and having a cylindrical surface as a detected surface disposed with a center axis thereof parallel to the rotating shaft, the rotary scale having a relative angle track formed circumferentially on the cylindrical surface to indicate relative angle information;
• a sensor head arranged to face the cylindrical surface of the rotary scale with an interval therebetween and configured to detect the relative angle track formed on the cylindrical surface of the rotary scale and output a detection signal corresponding to the relative angle track and varying in accordance with a size of the interval;
• and
• a first angle calculator configured to calculate a rotation angle of the rotary scale based on the detection signal output from the sensor head;
• an angle error storage storing an angle error corresponding to the size of the interval at each rotation angle calculated based on the detection signal output from the sensor head;
• and
• an angle compensator configured to compensate the rotation angle calculated by the first angle calculator of the rotary encoder, based on the angle error at each rotation angle stored in the angle error storage,
• the angle error stored in the angle error storage being the angle error corresponding to the size of the interval at each rotation angle calculated from the detection signal output from the sensor head based on a correlation between the size of the interval and a magnitude of the detection signal as well as the detection signal.

A rotation angle detection method of detecting a rotation angle of a rotating body as a detection target by using a rotary encoder, the rotary encoder including:

• a rotary scale connected to a rotating shaft of the rotating body and having a cylindrical surface as a detected surface disposed with a center axis thereof parallel to the rotating shaft and having a relative angle track formed circumferentially on the cylindrical surface to indicate relative angle information;
• a sensor head arranged to face the cylindrical surface of the rotary scale with an interval therebetween and configured to detect the relative angle track formed on the cylindrical surface of the rotary scale and output a detection signal corresponding to the relative angle track and varying in accordance with a size of the interval;
• and an angle calculator configured to calculate a rotation angle of the rotary scale based on the detection signal output from the sensor head,
• the method comprising:
• an angle error calculation step of calculating in advance an angle error corresponding to the size of the interval at each rotation angle calculated from the detection signal output from the sensor head based on a correlation between the size of the interval and a magnitude of the detection signal as well as the detection signal;
• and
• an angle compensation step of compensating the rotation angle of the rotary scale calculated based on the detection signal output from the sensor head, based on the angle error at a corresponding angle position calculated in the angle error calculation step.