Optical encoder having telecentric optical system

A reflection type optical reader module comprising;

• a light projecting source,
• an object lens used both for projecting and receiving light for irradiating light from the light projecting source to a graduation plate as parallel light in the form of a spot to include a group of graduation lines and gathering reflected light from the graduation plate,
• a light receiving portion arranged at an image plane of returning light from the object lens and including a light receiving array pattern in correspondence with images of a group of the graduation lines,
• an optical separator for transmitting projecting light from the light projecting source to the object lens and turning the returning light from the object lens to the light receiving portion including the light receiving array pattern, and
• a pin hole plate arranged at a focal position of the object lens on a returning light axis, wherein said returning light is turned via the optical separator and directed by the optical separator to the pin hole plate;
• wherein said light projecting source, said object lens, said light receiving portion, said optical separator, and said pin hole plate are integrally contained in a case having a window used both for projecting and receiving light, and
• wherein said reflection type optical reader module can be integrated to an optical encoder,
• wherein the light receiving portion includes a light blocking plate having a slit pattern in correspondence with the images of a group of the graduation lines and a light receiving element disposed on a back side of the light blocking plate for receiving light transmitted through the slit pattern and the light receiving array pattern is formed by exposing the light receiving element from the slit pattern.

A transmission type optical reader module comprising;

• a light projecting optical system including a light projecting source for irradiating light onto a face on one side of a graduation plate in the form of a spot to include a group of graduation lines,
• a light receiving optical system including a light receiving lens for gathering light transmitted through a face on an other side of the graduation plate,
• a pin hole plate arranged at a focal position on a front side of an optical axis of the light receiving lens, and
• a light receiving portion arranged at an image plane of light after passing through the pin hole plate and having a light receiving array pattern in correspondence with images of a group of graduation lines;
• wherein said light projecting optical system and said light receiving optical system are integrally contained in a case arranged oppositely together while interposing an air gap portion, wherein the graduation plate is inserted;
• and
• wherein said transmission type optical reader module can be integrated to an optical encoder.

A light receiving optical module comprising;

• a light receiving lens for gathering light transmitted through a graduation plate inscribed with a group of light transmitting graduation lines,
• a pin hole plate arranged at a focal position on a front side of an optical axis of the light receiving lens, and
• a light receiving portion arranged at an image plane of light after passing through the pin hole plate and having a light receiving array pattern in correspondence with images of the group of graduation lines,
• wherein said light receiving lens, said pin hole plate, and said light receiving portion are integrally contained in a case having a light receiving window;
• and
• wherein a transmission type reader can be constituted by integrating said light receiving optical module to an optical encoder along with a light projecting optical system,
• wherein the light receiving portion includes a light blocking plate having a slit pattern in correspondence with the images of a group of the graduation lines and a light receiving element disposed on a back side of the light blocking plate for receiving light transmitted through the slit pattern and the light receiving array pattern is formed by exposing the light receiving element from the slit pattern.