Image reading apparatus and document size detecting method

An image reading apparatus comprising:

• a document platen on which a document to be read is placed;
• a document platen cover, which is openably and closably attached to the document platen;
• an opening and closing detector configured to detect an open state and a closed state of the document platen cover;
• a reader including a light source configured to emit light to the document placed on the document platen and a light receiving portion configured to receive reflection light from the document, the reader being configured to read an image of the document in a main scanning direction according to the reflection light received by the light receiving portion;
• a document size determiner in which shading data for correcting a light intensity of the light emitted by the light source is set, the document size determiner configured to determine a size of the document from the image of the document read by the reader subjected to a shading correction using the shading data when the opening and closing detector detects the closed state of the document platen cover;
• a shading data obtaining device configured to obtain new shading data and set the new shading data in the document size determiner when the opening and closing detector detects the closed state of the document platen cover after the reader reads the image of the document;
• and
• a feeder configured to successively feed a plurality of documents to a reading position of the reader,
• wherein the shading data obtaining device does not obtain the new shading data when a number of documents successively read by the reader is equal to or smaller than a predetermined number.

An image reading apparatus comprising:

• a document platen on which a document to be read is placed;
• a document platen cover, which is openably and closably attached to the document platen;
• an opening and closing detector configured to detect an open state and a closed state of the document platen cover;
• a reader including a light source configured to emit light to the document placed on the document platen and a light receiving portion configured to receive reflection light from the document, the reader being configured to read an image of the document in a main scanning direction according to the reflection light received by the light receiving portion;
• a document size determiner in which shading data for correcting a light intensity of the light emitted by the light source is set, the document size determiner configured to determine a size of the document from the image of the document read by the reader subjected to a shading correction using the shading data when the opening and closing detector detects the closed state of the document platen cover;
• a shading data obtaining device configured to obtain new shading data and set the new shading data in the document size determiner when the opening and closing detector detects the closed state of the document platen cover after the reader reads the image of the document;
• and
• a temperature detector configured to detect a temperature of the reader,
• wherein the shading data obtaining device stores the temperature at a time when a previous shading data is obtained in the storage portion, and obtains the new shading data when a temperature difference between the temperature at a time when the opening and closing detector detects the closed state of the document platen cover and the temperature stored in the storage portion is equal to or larger than a predetermined temperature.

An image reading apparatus comprising:

• a document platen on which a document to be read is placed;
• a document platen cover, which is openably and closably attached to the document platen;
• an opening and closing detector configured to detect an open state and a closed state of the document platen cover;
• a reader including a light source configured to emit light to the document placed on the document platen and a light receiving portion configured to receive reflection light from the document, the reader being configured to read an image of the document in a main scanning direction according to the reflection light received by the light receiving portion;
• a document size determiner in which shading data for correcting a light intensity of the light emitted by the light source is set, the document size determiner configured to determine a size of the document from the image of the document read by the reader subjected to a shading correction using the shading data when the opening and closing detector detects the closed state of the document platen cover;
• a shading data obtaining device configured to obtain new shading data and set the new shading data in the document size determiner when the opening and closing detector detects the closed state of the document platen cover after the reader reads the image of the document;
• and
• a sub-scanning direction length detector provided at a predetermined distance, in a sub-scanning direction perpendicular to the main scanning direction, away from a reference position for the document to be placed on the document platen, the sub-scanning direction length detector being configured to detect a presence or absence of the document placed on the document platen,
• wherein the document size determiner determines the size of the document based on a detection result of the sub-scanning direction length detector and the size of the document in the main scanning direction.