Optical encoder including a plurality of phase adjusting gratings

Abstract

An optical encoder has a light source and a diffracted light interference device including at least first and second diffraction gratings confronting each other, producing diffracted light beams in specific orders by passing light emitted from the light source through the first and second diffraction gratings, and making the diffracted light beams in the specific orders, which have passed through the diffraction gratings, interfere with each other to produce on-axis interference light beams in which the sum of the orders of the diffraction at the diffraction gratings is zero and off-axis interference light beams in which the sum of the orders of the diffraction is not zero. A phase device is adjusting the phases of the on-axis interference light beams and the off-axis interference light beams emitted from plural portions of the diffracted light interference device. A plurality of light sensors receive and detect the on-axis interference light beams and the off-axis interference light beams device. In this structure, since the on-axis interference light beams in which the sum of the orders of the diffraction at the diffraction gratings is zero and the off-axis interference light beams in which the sum of the orders of the diffraction is not zero are produced and the phases of the on-axis interference light beams and the phases of the off-axis interference light beams are made equal to each other, unwanted negation of signals is avoided, whereby the light utilization efficiency is increased.

Dependencies are inferred from the claim text.