Rotary encoder having a sensor activation controller

Abstract

A rotary encoder comprising a code plate having an optical pattern, first sensor group A1 through An for detecting the rotational angle of the code plate by detecting the optical pattern, second sensor group B1 through Bn for detecting the rotational angle of the code plate by detecting the optical pattern. Each of the first sensors is associated with one of the second sensor, and the second sensor is positioned 180 degrees opposite to the associated first sensor along the circumference of the code plate. The rotary encoder further comprises a determination unit which determines if the output of the currently processed first or second sensor is in the first state, in which the rotational speed of the code plate relative to the currently processed first or second sensor is greater than a predetermined value, or in the second state, in which the rotational speed of the code plate relative to the currently processed first or second sensor is smaller than or equal to the predetermined value. If it is determined that the output is in one of the first and second states which was defined in advance, a controller activates either the first group sensors or the second group sensors. If it is determined that the output is in the other state, then the controller activates both the first and second group sensors.