Importance

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Abstract

An encoder including a code carrying medium movable with respect to a photoelectrical sensor in one direction, the code carrying medium having a first track formed with a plurality of first blocks arranged along the aforementioned direction of movement of the code carrying medium, each of the first blocks carrying address information of the particular block recorded in a direction crossing the direction of movement of the code carrying medium, and a second track parallel with the first track and formed with a plurality of second blocks arranged along the direction of movement, each of the second blocks carrying reference position information representing a reference position of the particular one of the second blocks and a plurality of coded bar patterns arranged with a first predetermined pitch in series along the direction of movement of the code carrying medium. The photoelectrical sensor has a plurality of sensing elements arranged in series with a second predetermined pitch which is slightly different from the first predetermined pitch of the coded bar patterns to produce a vernier relationship with the coded bar patterns. The photoelectrical sensor is arranged with respect to the code carrying medium so that the sensing elements in the sensor read the information and patterns on the code carrying medium to produce an output representing a relative movement between the code carrying medium and the photoelectrical sensor.

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First Claim