Encoder including a light detecting device having two signal processing sections for pixels in a first and second direction

An encoder comprising:

• a scale plate arranged movably in a predetermined operational direction;
• a plurality of light relay portions which are formed along the operational direction in the scale plate and each of which is comprised of a one-dimensional array of some of light propagation portions and light nonpropagation portions arranged in a direction perpendicular to the operational direction;
• a light source device for projecting light toward the light relay portions;
• and
• a light detecting device which is arranged to receive the light projected by the light source device, through one or two of the light relay portions, which has a light receiving region comprised of a two-dimensional array of pixels arranged in the operational direction and in the direction perpendicular to the operational direction, and which outputs light intensity profile data indicating a one-dimensional profile of intensity of incident light in each of the operational direction and the direction perpendicular to the operational direction;
• and
• a processing unit for finding an operation absolute value of the scale plate;
• wherein each of the light relay portions has a pattern of the one-dimensional array of some of the light propagation portions and light nonpropagation portions different from those of the other light relay portions;
• wherein reference light propagation portions are formed in the scale plate and on respective first lines passing the corresponding light relay portions along the direction perpendicular to the operational direction;
• wherein the processing unit is configured to identify the light relay portion having relayed the light from the light source device to the light detecting device, with respect to a position of the reference light propagation portion, based on the light intensity profile data in the direction perpendicular to the operational direction, thereafter to calculate a position of the light relay portion relative to a reference position in the light receiving region, based on the light intensity profile data in the operational direction, and to find the operation absolute value of the scale plate from the position of the light relay portion;
• wherein the light relay portions comprise a plurality of light relay portions formed on a second line along the operational direction, and wherein between the light relay portions adjacent to each other, their patterns of the one-dimensional arrays of some of the light propagation portions and light nonpropagation portions are different in one place from each other;
• wherein the light detecting device is a profile sensor, and the profile sensor has the light receiving region, a first signal processing section, and a second signal processing section;
• wherein the light receiving region comprises a two-dimensional array consisting of M×N pixels arranged in the operational direction and in the direction perpendicular to the operational direction, a pixel at a position of the mth row and the nth column is composed of two photodiodes, each of M and N is an integer of not less than 2, m is an arbitrary integer between 1 and M both inclusive, and n is an arbitrary integer between 1 and N both inclusive;
• wherein an anode terminal of each photodiode is grounded, cathode terminals of M photodiodes in the nth column are connected through a common wire to the first signal processing section, and cathode terminals of N photodiodes in the mth row are connected through a common wire to the second signal processing section;
• wherein the processing unit calculates the number of regions over a first predetermined threshold on the basis of the light intensity profile data in the operational direction, and determines the number of light relay portions located on the light receiving region;
• wherein the processing unit identifies the light relay portion having relayed the light from the light source device to the light detecting device by using a second predetermined threshold and a third predetermined threshold, with respect to a position of the reference light propagation portion, based on the light intensity profile data in the direction perpendicular to the operational direction, the second predetermined threshold is defined as a determination standard of brightness in a case where there is one light propagation portion along the operational direction, and the third predetermined threshold is defined as a determination standard of brightness in the case where there are two light propagation portions along the operational direction;
• and
• wherein the processing unit calculates a position of the light relay portion relative to a reference position in the light receiving region by calculating a center-of-gravity position of a region or regions over the first predetermined threshold, based on the first light intensity profile data in the operational direction, and finds an operation absolute value of the scale plate from the position of the light relay portion.