Image reading device and focus adjustment method thereof

A focus adjusting method of an image reading apparatus in which light sent from a document is condensed by a condenser lens and converted into an electric signal by an optical sensor, the focus adjusting method comprising the steps of:

• (a) moving the condenser lens and the optical sensor integrally so as to adjust an optical path length between the document and the condenser lens;
• (b) reading luminance of a reading line on the document by the optical sensor and converting the luminance into an electric signal;
• (c) calculating a value showing the degree of focusing by the electric signal obtained in step (b);
• (d) repeating steps (a), (b) and (c) by a plurality of optical path lengths;
• (e) finding an optical path length by which the value showing the degree of focusing is maximized;
• and
• (f) adjusting an optical path length so that it is the optical path length found in step (e).

An image reading apparatus comprising:

• a condenser lens for condensing light sent from a document;
• a line sensor having a plurality of photoelectric transfer elements for converting light sent from the condenser lens into an electric signal;
• an optical path length adjusting means for adjusting an optical path length between the document and the condenser lens;
• a calculating means for storing a signal obtained when the line sensor reads a plurality of reading lines on the document and also for calculating a value showing the degree of focusing at each line;
• and
• a control means for giving a command to the optical path length adjusting means so that a sum of the values showing the degree of focusing on a plurality of lines is maximized.

A focus adjusting method of an image reading apparatus in which light sent from a document is condensed by a condenser lens and converted into an electric signal by a line sensor composed of a plurality of photoelectric transfer elements comprising the steps of:

• (a) adjusting an optical path length between the condenser lens and the document;
• (b) reading a plurality of lines on the document by the line sensor and calculating a value showing the degree of focusing on each line;
• (c) repeating processes (a) and (b) by a plurality of optical path lengths;
• (d) finding an optical path length by which a value showing the degree of focusing is maximized on the plurality of lines;
• and
• (e) adjusting an optical path length between the condenser lens and the document so that it is the optical path length found in step (d).

An image reading apparatus comprising:

• a condenser lens for condensing light sent from a document;
• a line sensor having a plurality of photoelectric transfer elements for converting light sent from the condenser lens into an electric signal;
• an optical path length adjusting means for adjusting an optical path length between the document and the condenser lens;
• and
• a means for correcting positions of the photoelectric transfer elements on the line sensor used for reading according to the optical path length.

A focus adjusting method of an image reading apparatus in which light sent from a document is condensed by a condenser lens and converted into an electric signal by a line sensor composed of a plurality of photoelectric transfer elements comprising the steps of:

• (a) adjusting an optical path length between the condenser lens and the document;
• (b) correcting positions of the photoelectric transfer elements on the line sensor used for reading according to the optical path length;
• (c) calculating a value showing a value of the degree of focusing when the document is read by the photoelectric transfer elements located at the corrected positions on the line sensor;
• (d) repeating steps (b) and (c) by a plurality of optical path lengths;
• (e) finding an optical path length by which a value showing the degree of focusing is maximized;
• and
• (f) adjusting an optical path length between the condenser lens and the document so that it is the optical path length found in step (e).